[docker ci] Revert "parallel" builds in seperate actions (#4057)

- Broke tagging images together
- Saved only a few mins
  - x86_64 build is fast, time is all spent on cross compile of arm64
- Also remove evil copy pasta ... which is nice

Was worth an attempt.

.github/workflows/docker_amd64.yml → .github/workflows/docker.yml

@@ -1,4 +1,4 @@
-name: docker amd64 (x86_64)
+name: docker
 
 on:
   push:
@@ -39,7 +39,7 @@ jobs:
         uses: docker/build-push-action@v5
         with:
           context: .
-          platforms: linux/amd64
+          platforms: linux/amd64,linux/arm64
           push: true
           tags: pyfound/black:latest,pyfound/black:${{ env.GIT_TAG }}
 
@@ -50,7 +50,7 @@ jobs:
         uses: docker/build-push-action@v5
         with:
           context: .
-          platforms: linux/amd64
+          platforms: linux/amd64,linux/arm64
           push: true
           tags: pyfound/black:latest_release
 
@@ -61,7 +61,7 @@ jobs:
         uses: docker/build-push-action@v5
         with:
           context: .
-          platforms: linux/amd64
+          platforms: linux/amd64,linux/arm64
           push: true
           tags: pyfound/black:latest_prerelease