Pull dvc baseline images from gmt-6.4 branch to test GMT dev (#1865)

Co-authored-by: Dongdong Tian <[email protected]>

Author: weiji14

.github/workflows/ci_tests_dev.yaml

@@ -106,8 +106,12 @@ jobs:
       # Pull baseline image data from dvc remote (DAGsHub)
       - name: Pull baseline image data from dvc remote
         run: |
+          ORIGINAL_BRANCH=$(git branch --show-current)
+          # Pull down GMT 6.4 baseline images from the gmt-6.4 branch
+          git checkout gmt-6.4
           dvc pull
           ls -lhR pygmt/tests/baseline/
+          git checkout ${ORIGINAL_BRANCH}
 
       # Build and install latest GMT from GitHub
       - name: Install GMT ${{ matrix.gmt_git_ref }} branch (Linux/macOS)