CI: Enforce code format check on PR merge

**Is your feature request related to a problem? Please describe.**
Right now the master branch is in a state where a clean build causes files to be auto formatted. This means during every change people need to make sure not to include auto format changes not related to their work.

To reproduce run `./auron-build.sh --sparkver 3.5 --scalaver 2.12 --pre` on master head (241c8069839d10fcc0bcdd8e3f41a0890e94eb9a)

**Describe the solution you'd like**
Run the format check during the PR checks and fail it if there are format changes that are not checked in.

**Describe alternatives you've considered**
No

**Additional context**
None