Only use kn-main if the ref has a kn- prefix

Author: lauzadis

.github/actions/checkout-head/action.yml

@@ -49,7 +49,7 @@ runs:
           echo "ref=$ref" >> "$GITHUB_OUTPUT"
         else
           baseref="main"
-          if git ls-remote --exit-code --heads "https://github.com/$REPOSITORY.git" "kn-main"; then
+          if [[ "$ref" == kn-* ]] && git ls-remote --exit-code --heads "https://github.com/$REPOSITORY.git" "kn-main"; then
             baseref="kn-main"
           elif [ -n "$GITHUB_BASE_REF" ]; then
             echo "attempting GH base ref: $GITHUB_BASE_REF"