feat: enable npm cache by default to reduce 403 errors (#1092)

* feat: enable npm cache by default to reduce 403 errors

Add npm_cache input (default: "true") and actions/cache step for ~/.npm
to avoid downloading renovate from npm registry on every run, reducing
403 Forbidden errors and speeding up installation.

Close #1091

* test

Author: suzuki-shunsuke

.github/workflows/test.yaml

@@ -39,3 +39,7 @@ jobs:
         uses: ./
         with:
           config_file_path: ${{ steps.files.outputs.files }}
+      - name: Test with npm_cache disabled
+        uses: ./
+        with:
+          npm_cache: "false"

action.yaml

@@ -37,13 +37,24 @@ inputs:
 
       You can specify multiple files by multiple lines.
     required: false
+  npm_cache:
+    description: |
+      Enable npm cache to speed up the installation of renovate.
+      If it's "true", the npm cache is enabled.
+    default: "true"
+    required: false
 runs:
   using: composite
   steps:
     - uses: actions/setup-node@6044e13b5dc448c55e2357c09f80417699197238 # v6.2.0
       if: inputs.node-version != 'none'
       with:
         node-version: ${{inputs.node-version}}
+    - uses: actions/cache@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
+      if: inputs.npm_cache == 'true'
+      with:
+        path: ~/.npm
+        key: renovate-npm-${{ runner.os }}
     - name: Validate Renovate Configuration with renovate-config-validator
       run: |
         set -eu