.github/workflows/tests.yml: Deploy Docker image

Deploy the latest Docker image on a push to master.
Deploy a tagged Docker image upon publication of a release.

.github/workflows/tests.yml

@@ -3,6 +3,9 @@ on:
   push:
     branches: master
   pull_request: []
+  release:
+    types:
+      - published
 jobs:
   tests:
     if: github.repository == 'Homebrew/brew'
@@ -140,6 +143,22 @@ jobs:
       run: |
         if [ "$RUNNER_OS" = "Linux" ]; then
           docker-compose -f Dockerfile.yml run --rm -v $GITHUB_WORKSPACE:/tmp/test-bot sut
+          docker tag homebrew_sut brew
         else
           brew test-bot
         fi
+
+    - name: Deploy the latest Docker image
+      if: matrix.os == 'ubuntu-latest' && github.ref == 'refs/heads/master'
+      run: |
+        docker login docker.pkg.github.com -u BrewTestBot -p ${{secrets.GITHUB_TOKEN}}
+        docker tag brew docker.pkg.github.com/homebrew/brew/brew
+        docker push docker.pkg.github.com/homebrew/brew/brew
+
+    - name: Deploy the tagged Docker image
+      if: matrix.os == 'ubuntu-latest' && startsWith(github.ref, 'refs/tags/')
+      run: |
+        docker login docker.pkg.github.com -u BrewTestBot -p ${{secrets.GITHUB_TOKEN}}
+        v=${GITHUB_REF:10}
+        docker tag brew "docker.pkg.github.com/homebrew/brew/brew:$v"
+        docker push "docker.pkg.github.com/homebrew/brew/brew:$v"