set github-actions git credentials

Author: kernc

.github/deploy-gh-pages.sh

@@ -32,6 +32,12 @@ if git diff --staged --quiet; then
   echo "$0: No changes to commit."
   exit 0
 fi
+
+if ! git config user.name; then
+    git config user.name 'github-actions'
+    git config user.email '41898282+github-actions[bot]@users.noreply.github.com'
+fi
+
 git commit -a -m "CI: Update docs for ${GITHUB_REF#refs/tags/} ($head)"