ci: use repo variables for lint and cache-depends-sources runners

Use `vars.RUNNER_AMD64` and `vars.RUNNER_ARM64` repo variables with
GitHub-hosted runner fallback defaults, matching the pattern from the
main build pipeline PR.

- cache-depends-sources.yml: ${{ vars.RUNNER_ARM64 || 'ubuntu-24.04-arm' }}
- lint.yml: ${{ vars.RUNNER_AMD64 || 'ubuntu-24.04' }}

Author: thepastaclaw

.github/workflows/cache-depends-sources.yml

@@ -9,7 +9,7 @@ on:
 jobs:
   cache-sources:
     name: Cache depends sources
-    runs-on: ubuntu-24.04-arm
+    runs-on: ${{ vars.RUNNER_ARM64 || 'ubuntu-24.04-arm' }}
     steps:
       - name: Checkout code
         uses: actions/checkout@v4

.github/workflows/lint.yml

@@ -11,7 +11,7 @@ on:
 jobs:
   lint:
     name: Run linters
-    runs-on: ubuntu-24.04
+    runs-on: ${{ vars.RUNNER_AMD64 || 'ubuntu-24.04' }}
     container:
       image: ${{ inputs.container-path }}
       options: --user root