Update environment variable to get current branch name, instead of pull request identifier, when the workflow is triggered by a PR

Author: villegar

.github/workflows/R-CMD-check.yaml

@@ -28,6 +28,7 @@ jobs:
     env:
       GITHUB_PAT: ${{ secrets.GITHUB_TOKEN }}
       R_KEEP_PKG_SOURCE: yes
+      BRANCH_NAME: ${{ github.head_ref || github.ref_name }} 
 
     steps:
       - uses: actions/checkout@v4
@@ -49,7 +50,7 @@ jobs:
         uses: actions/checkout@v4
         with:
           repository: ${{ github.repository_owner }}/dsBase
-          ref: ${{ github.ref_name }}
+          ref: ${{ env.BRANCH_NAME }}
           path: dsBase
 
       - name: Install dsBase