Skip the rebuild when rector-src main is a release tag commit

A tagged main is already published by the tag build of rector-src. A
dispatched build would race that build for the push to rectorphp/rector,
and the loser of the race fails on a non fast forward push.

Tags are resolved with git ls-remote, which lists a lightweight tag with
the commit itself and an annotated tag with an extra "^{}" line, so both
kinds are matched. rector-src has 36 annotated tags among 574.

Author: TomasVotruba

.github/workflows/dispatch_build_scoped_rector.yaml

@@ -15,8 +15,29 @@ jobs:
         runs-on: ubuntu-latest
 
         steps:
+            # a tagged main is already being published by the tag build of rector-src,
+            # dispatching a second build would race it for the push to rectorphp/rector
+            -
+                name: "Check whether rector-src main is a release tag commit"
+                id: release_tag
+                run: |
+                    RECTOR_SRC="https://github.com/rectorphp/rector-src.git"
+
+                    MAIN_SHA=$(git ls-remote $RECTOR_SRC refs/heads/main | cut -f1)
+                    if [ -z "$MAIN_SHA" ]; then
+                        echo "Could not resolve rector-src main"
+                        exit 1
+                    fi
+
+                    # lightweight tags are listed with the commit itself, annotated ones with a "^{}" line
+                    if git ls-remote --tags $RECTOR_SRC | grep -q "^${MAIN_SHA}"; then
+                        echo "rector-src main $MAIN_SHA is tagged, leaving the build to the tag itself"
+                        echo "tagged=true" >> $GITHUB_OUTPUT
+                    fi
+
             -
                 name: "Trigger build_scoped_rector.yaml in rectorphp/rector-src"
+                if: steps.release_tag.outputs.tagged != 'true'
                 env:
                     GH_TOKEN: ${{ secrets.ACCESS_TOKEN }}
                 run: gh workflow run build_scoped_rector.yaml --repo rectorphp/rector-src --ref main