Fix test_regrtest when run with uops always on (#108778)

The fix has two parts:
- When `-X uops` is detected, pass it on to the subprocess created to run the manufactured test.
  I need this so I can run `./python -Xuops -m test test_regrtest` and see it fail without the next fix.
- Use `-R 6:3:` in `ArgsTestCase.test_huntrleaks` instead of `-R 3:3:` -- it takes longer to settle with `-X uops`.