Only upload once

Author: seisman

.github/workflows/ci_docs.yml

@@ -146,6 +146,7 @@ jobs:
         with:
           name: pygmt-docs-pdf
           path: doc/_build/latex/pygmt.pdf
+        if: matrix.os == 'ubuntu-latest'
 
       - name: Checkout the gh-pages branch
         uses: actions/[email protected]