Fix CI incorrectly tagging RC releases and disables docker builds on forks (#686)

* properly tag rc releases

* avoid builds on forked prs

* simplify condition

.github/workflows/_buildx.yml

@@ -26,10 +26,9 @@ jobs:
       - name: Prepare master push tags
         if: github.event_name == 'push' && github.ref == 'refs/heads/master'
         run: |
-          echo "tag_flags=--tag ${{ github.ref }}" >> $GITHUB_ENV
           REPO=ghcr.io/${{ github.repository }}
           TAG=$(git describe --tags)
-          if [ -z "$(git tag --points-at HEAD)" ]
+          if [ -z "$(git tag --points-at HEAD)" ] || [ "$TAG" == *"rc"* ]
           then
             TAG2="dev"
           else

.github/workflows/pull_request.yml

@@ -19,4 +19,6 @@ jobs:
     uses: ./.github/workflows/_gorelease.yml
   call-buildx:
     needs: call-gorelease
+    # only build on pull requests from the same repo for now
+    if: github.event.pull_request.head.repo.full_name == github.repository
     uses: ./.github/workflows/_buildx.yml