feat: Use relative paths to reference sub-actions in composite actions (#59)

Fixes
github/continuous-ai-for-accessibility#87
(Hubber access only)
Fixes
github/continuous-ai-for-accessibility#81
(Hubber access only)

### Problem

`uses: github/accessibility-scanner@main` currently fails with the
following error—

> Error: Can't find 'action.yml', 'action.yaml' or 'Dockerfile' under
'/home/runner/work/accessibility-sandbox/accessibility-sandbox/.github/actions/gh-cache/cache'.
Did you forget to run actions/checkout before running your local action?

—this PR makes it work.

### Solution

This PR basically moves the preparatory `cp` workflow step [we used to
require](https://github.com/github/accessibility-scanner/tree/bc0c7650825e578c243347fe551f247826bcb70e?tab=readme-ov-file#1-add-a-workflow-file)
into the composite action(s) itself.

This PR is a superior alternative to
c262469:
1. It restores our ability to merge `main` directly into `v2`, which
simplifies backports (e.g. dependency updates that Dependabot opens for
`main`).
2. It means referencing a point release (e.g. `uses:
github/[email protected]`) _only_ runs code from that release
(rather than a mix of `v2.4.0` and (newer) `v2` code).

### Testing

- I tested using `uses:
github/accessibility-scanner@smockle/restore-relative-paths`, and it
worked:
https://github.com/github/accessibility-sandbox/actions/runs/18943849865
(Hubber access only)
- I tested using a sub-action directly (e.g. `uses:
github/accessibility-scanner/.github/actions/gh-cache/cache@smockle/restore-relative-paths`),
and it worked:
https://github.com/github/accessibility-sandbox/actions/runs/18945624950
(Hubber access only)
- The “Test” CI check passed:
https://github.com/github/accessibility-scanner/actions/runs/18944419202/job/54092648187?pr=59

Author: smockle

.github/actions/gh-cache/cache/action.yml

@@ -14,7 +14,7 @@ inputs:
   fail_on_cache_miss:
     description: "Fail the workflow if cached item is not found."
     required: false
-    default: 'false'
+    default: "false"
 
 outputs:
   value:
@@ -24,8 +24,15 @@ outputs:
 runs:
   using: "composite"
   steps:
+    - name: Make sub-actions referenceable
+      working-directory: ${{ github.action_path }}
+      shell: bash
+      run: |
+        mkdir -p /home/runner/work/_actions/current/.github/actions
+        rsync -a ../../../../.github/actions/ /home/runner/work/_actions/current/.github/actions/
+        ls -ltra /home/runner/work/_actions/current/.github/actions
     - name: Restore cached value
-      uses: ./.github/actions/gh-cache/restore
+      uses: ./../../_actions/current/.github/actions/gh-cache/restore
       with:
         path: ${{ inputs.key }}
         token: ${{ inputs.token }}
@@ -41,7 +48,7 @@ runs:
 
     - if: ${{ inputs.value }}
       name: Save cached value
-      uses: ./.github/actions/gh-cache/save
+      uses: ./../../_actions/current/.github/actions/gh-cache/save
       with:
         path: ${{ inputs.key }}
         token: ${{ inputs.token }}

action.yml

@@ -40,9 +40,16 @@ outputs:
 runs:
   using: "composite"
   steps:
+    - name: Make sub-actions referenceable
+      working-directory: ${{ github.action_path }}
+      shell: bash
+      run: |
+        mkdir -p /home/runner/work/_actions/current/.github/actions
+        rsync -a .github/actions/ /home/runner/work/_actions/current/.github/actions/
+        ls -ltra /home/runner/work/_actions/current/.github/actions
     - name: Restore cached results
       id: restore
-      uses: ./.github/actions/gh-cache/cache
+      uses: ./../../_actions/current/.github/actions/gh-cache/cache
       with:
         key: ${{ inputs.cache_key }}
         token: ${{ inputs.token }}
@@ -59,20 +66,20 @@ runs:
     - if: ${{ inputs.login_url && inputs.username && inputs.password && !inputs.auth_context }}
       name: Authenticate
       id: auth
-      uses: ./.github/actions/auth
+      uses: ./../../_actions/current/.github/actions/auth
       with:
         login_url: ${{ inputs.login_url }}
         username: ${{ inputs.username }}
         password: ${{ inputs.password }}
     - name: Find
       id: find
-      uses: ./.github/actions/find
+      uses: ./../../_actions/current/.github/actions/find
       with:
         urls: ${{ inputs.urls }}
         auth_context: ${{ inputs.auth_context || steps.auth.outputs.auth_context }}
     - name: File
       id: file
-      uses: ./.github/actions/file
+      uses: ./../../_actions/current/.github/actions/file
       with:
         findings: ${{ steps.find.outputs.findings }}
         repository: ${{ inputs.repository }}
@@ -89,7 +96,7 @@ runs:
     - if: ${{ inputs.skip_copilot_assignment != 'true' }}
       name: Fix
       id: fix
-      uses: ./.github/actions/fix
+      uses: ./../../_actions/current/.github/actions/fix
       with:
         issues: ${{ steps.get_issues_from_filings.outputs.issues }}
         repository: ${{ inputs.repository }}
@@ -119,7 +126,7 @@ runs:
         FILINGS: ${{ steps.file.outputs.filings }}
         FIXINGS: ${{ steps.fix.outputs.fixings }}
     - name: Save cached results
-      uses: ./.github/actions/gh-cache/cache
+      uses: ./../../_actions/current/.github/actions/gh-cache/cache
       with:
         key: ${{ inputs.cache_key }}
         value: ${{ steps.results.outputs.results }}