Make CI check to produce a patch file

.gitlab-ci.yml

@@ -15,4 +15,17 @@ run-checks:
     - pip install pre-commit
     - pre-commit --version
     - git fetch origin master
-    - pre-commit run --from-ref FETCH_HEAD --to-ref HEAD
+    - if ! pre-commit run --from-ref FETCH_HEAD --to-ref HEAD ; then
+    -   git config user.name "Gitlab CI"
+    -   git config user.email noreply@cern.ch
+    -   git add -u
+    -   git commit --message "Automatic fixes" --message "see $CI_JOB_URL" &&
+        git format-patch -1 --stdout > hooks_changes.patch &&
+        echo -e "Apply fixes with:\n\n  curl $CI_JOB_URL/artifacts/raw/hooks_changes.patch | git am"
+    -   exit 1
+    - fi
+  artifacts:
+    expose_as: "CI check patch"
+    paths:
+      - hooks_changes.patch
+    when: on_failure