fix(gha): fix branch detection error (#6350)

from e.g. https://github.com/spinnaker/clouddriver/actions/runs/13418069226/job/37483771864

Run BRANCHES=$(git branch -r --contains refs/tags/v5.91.0)
BRANCHES is '  origin/HEAD -> origin/master
  origin/master'
NUM_BRANCHES is '2'
exactly one branch required to release clouddriver, but there are 2 (  origin/HEAD -> origin/master
  origin/master)

.github/workflows/release.yml

@@ -23,7 +23,7 @@ jobs:
       # Given a tag, determine what branch we are on, so we can bump dependencies (or not)
       - name: Get Branch
         run: |
-          BRANCHES=$(git branch -r --contains ${{ github.ref }})
+          BRANCHES=$(git branch -r --contains ${{ github.ref }} | grep -v 'HEAD')
           echo "BRANCHES is '${BRANCHES}'"
           # Check for no branches explicitly...Otherwise echo adds a newline so wc thinks there's
           # one branch.  And echo -n makes it appears that there's one less branch than there