add checkout so .git is avalible for bind

drop platforms from dryrun

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

@@ -16,16 +16,16 @@ jobs:
     needs: files-changed
     runs-on: ubuntu-latest
     steps:
+      - uses: actions/checkout@v5
       - uses: docker/setup-buildx-action@v3
       - name: Build regular container image
         uses: docker/build-push-action@v5
         with:
           push: false
           tags: gitea/gitea:linux-amd64
-          platforms: linux/amd64,linux/arm64,linux/riscv64
       - name: Build rootless container image
         uses: docker/build-push-action@v5
         with:
           push: false
           file: Dockerfile.rootless
-          tags: gitea/gitea:linux-amd64,linux/arm64,linux/riscv64
+          tags: gitea/gitea:linux-amd64