CI: Skip later CI on reformat

Small chance a bug gets through, but this will avoid multiple runs on the
common case of reformatting users' pull requests, and related run
cancellation problems.

.github/workflows/format.yml

@@ -38,11 +38,11 @@ jobs:
           ./configure
           make venv
           source .venv/bin/activate
-          make -j 2 format CLANGFORMAT=clang-format-18
+          make -j 4 format CLANGFORMAT=clang-format-18
           git status
       - name: Push
         run: |-
           if [ -n "$(git status --porcelain)" ]; then
-            git commit . -m "Apply 'make format'" &&
+            git commit . -m "Apply 'make format' [ci skip]" &&
             git push origin
           fi