Add format:verify back to GitHub Actions push.yml

I removed it from https://github.com/JoshuaKGoldberg/TypeStat/pull/1011 because it constantly complained about at least one file being off in a way I couldn't figure out. Annoying.

https://github.com/JoshuaKGoldberg/TypeStat/runs/4129272214?check_suite_focus=true

```
$ yarn prettier --list-different "**/*.{js,json,md,ts,yml}"
$ /home/runner/work/TypeStat/TypeStat/node_modules/.bin/prettier --list-different '**/*.{js,json,md,ts,yml}'
src/mutations/typeMutating/createNonNullAssertion.ts
error Command failed with exit code 1.
```

Start in push.yml and review the removed format:verify step alongside the linked GitHub Actions run. Run the reported yarn prettier --list-different command and inspect src/mutations/typeMutating/createNonNullAssertion.ts. Done means the verification step is restored and the push workflow no longer fails on the reported formatting difference.

Written by the indexing model from the issue text.