Use native ARM runners for ARM Docker image builds

[Copilot]

ARM images were built via QEMU emulation on x86 runners. This replaces emulation with native ARM compilation on ubuntu-24.04-arm runners.

Implementation

• Matrix strategy with platform-specific runners:

  • linux/amd64 → ubuntu-latest
  • linux/arm64 → ubuntu-24.04-arm
  • linux/arm/v7 → ubuntu-24.04-arm

• Digest-based workflow:

  1. Build jobs push platform images by digest
  2. Artifacts upload digests (digests-{amd64,arm64,armv7})
  3. Merge job creates multi-platform manifest from digests

• Cache scoping by platform (build-${{ matrix.platform }})

• Removed QEMU setup step

Changes

Both docker_build.yml and docker_frankenphp.yml workflows modified:

jobs:
  build:
    strategy:
      matrix:
        include:
          - platform: linux/amd64
            runner: ubuntu-latest
            platform-slug: amd64
          - platform: linux/arm64
            runner: ubuntu-24.04-arm
            platform-slug: arm64
          - platform: linux/arm/v7
            runner: ubuntu-24.04-arm
            platform-slug: armv7
    runs-on: ${{ matrix.runner }}
    steps:
      # ... build and push by digest
      
  merge:
    needs: build
    steps:
      # ... merge digests into multi-platform manifest

Parallel native builds replace sequential emulated builds. Final images remain identical.

---

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 54.77%. Comparing base (7069af4) to head (8ebc822).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1248      +/-   ##
============================================
- Coverage     54.77%   54.77%   -0.01%     
  Complexity     8012     8012              
============================================
  Files           601      601              
  Lines         25691    25691              
============================================
- Hits          14073    14071       -2     
- Misses        11618    11620       +2     

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