Bump alpine to 3.23, add platforms to docker-dryrun (#36379)

- Bump alpine to 3.23 following
https://github.com/go-gitea/gitea/pull/36185 and
https://github.com/go-gitea/gitea/pull/36202.
- Enable all architectures in `docker-dryrun`.
- Tweak actions conditions to be more precise.

---------

Signed-off-by: silverwind <me@silverwind.io>
Co-authored-by: techknowlogick <techknowlogick@gitea.com>
Co-authored-by: Giteabot <teabot@gitea.io>

.github/workflows/files-changed.yml

@@ -85,6 +85,7 @@ jobs:
               - "uv.lock"
 
             docker:
+              - ".github/workflows/pull-docker-dryrun.yml"
               - "Dockerfile"
               - "Dockerfile.rootless"
               - "docker/**"

.github/workflows/pull-docker-dryrun.yml

@@ -14,24 +14,25 @@ jobs:
       contents: read
 
   container:
-    if: needs.files-changed.outputs.docker == 'true' || needs.files-changed.outputs.actions == 'true'
+    if: needs.files-changed.outputs.docker == 'true'
     needs: files-changed
     runs-on: ubuntu-latest
     permissions:
       contents: read
     steps:
       - uses: actions/checkout@v6
+      - uses: docker/setup-qemu-action@v3
       - uses: docker/setup-buildx-action@v3
       - name: Build regular container image
         uses: docker/build-push-action@v6
         with:
           context: .
+          platforms: linux/amd64,linux/arm64,linux/riscv64
           push: false
-          tags: gitea/gitea:linux-amd64
       - name: Build rootless container image
         uses: docker/build-push-action@v6
         with:
           context: .
           push: false
+          platforms: linux/amd64,linux/arm64,linux/riscv64
           file: Dockerfile.rootless
-          tags: gitea/gitea:linux-amd64