update ci workflow to add target_branch param

.github/workflows/taosd-ci.yml

@@ -35,6 +35,7 @@ jobs:
         id: parameters
         run: |
           set -euo pipefail
+          target_branch=${{ github.event.pull_request.base.ref }}
           # check whether to run tdgpt test cases
           cd ${{ env.WKC }}
           changed_files_non_doc=$(git --no-pager diff --name-only FETCH_HEAD $(git merge-base FETCH_HEAD $target_branch) | grep -v "^docs/en/" | grep -v "^docs/zh/" | grep -v ".md$" | tr '\n' ' ' || :)