gh-100072: only trigger netlify builds for doc changes (#100074)

Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com>

netlify.toml

@@ -2,6 +2,9 @@
     base = "Doc/"
     command = "make html"
     publish = "build/html"
+    # Do not trigger netlify builds if docs were not changed.
+    # Changed files should be in sync with `.github/workflows/doc.yml`
+    ignore = "git diff --quiet $CACHED_COMMIT_REF $COMMIT_REF . ../netlify.toml"
 
 [build.environment]
   PYTHON_VERSION = "3.8"