ci: detect remote default branch

Author: johnhuang316

.github/workflows/publish-to-pypi.yml

@@ -26,11 +26,15 @@ jobs:
           fetch-depth: 0
           ref: ${{ env.RELEASE_REF }}
 
-      - name: Ensure tag is published from main
+      - name: Ensure tag points to default branch
         run: |
-          git fetch origin main
-          if ! git merge-base --is-ancestor "$(git rev-parse HEAD)" origin/main; then
-            echo "::error::Release tag must point to a commit reachable from main"
+          git fetch origin
+          TARGET_BRANCH=$(git remote show origin | awk '/HEAD branch/ {print $NF}')
+          if [ -z "$TARGET_BRANCH" ]; then
+            TARGET_BRANCH=master
+          fi
+          if ! git merge-base --is-ancestor "$(git rev-parse HEAD)" "origin/${TARGET_BRANCH}"; then
+            echo "::error::Release tag must point to a commit reachable from ${TARGET_BRANCH}"
             exit 1
           fi