CI: Exclude naturalearth URL in gallery examples from workflow check links (#4351)

Author: yvonnefroehlich

.github/workflows/check-links.yml

@@ -63,6 +63,7 @@ jobs:
           --exclude "^https://hackmd.io/@pygmt"
           --exclude "^https://test.pypi.org/simple/"
           --exclude "^https://www.adobe.com/jp/print/postscript/pdfs/PLRM.pdf"
+          --exclude "^https://naciscdn.org/naturalearth"
           --exclude "^https://www.generic-mapping-tools.org/remote-datasets/%s$"
           --exclude "^https://www.gnu.org/software/libc/manual/html_node/TZ-Variable.html"
           --exclude "^https://www.pygmt.org/%7B%7Bpath%7D%7D"