Make the CI show the proposed modifications of ufmt on fail (#4791)

* Show git diff after lint run

* break both flake8 and ufmt

* Make it run on fail

* Undo breaks and fix job message.

.circleci/config.yml

@@ -187,6 +187,10 @@ jobs:
             pip install --user --progress-bar off pre-commit
             pre-commit install-hooks
       - run: pre-commit run --all-files
+      - run:
+          name: Required lint modifications
+          when: on_fail
+          command: git diff
 
   python_type_check:
     docker:

.circleci/config.yml.in

@@ -187,6 +187,10 @@ jobs:
             pip install --user --progress-bar off pre-commit
             pre-commit install-hooks
       - run: pre-commit run --all-files
+      - run:
+          name: Required lint modifications
+          when: on_fail
+          command: git diff
 
   python_type_check:
     docker: