Fix unittest rerun logic when checking for skipped tests (#90888)
I made an important mistake here when thinking `not result.skipped` mean that the current test wasn't skipped.
Similar to `result.failures` or `result.errors`, `result.skipped` is that it's a list including all the skipped messages so far in the test suite (https://docs.python.org/3/library/unittest.html#unittest.TestResult). As such, the correct way to check if the current test was skipped is to compare `skipped_before` and `len(result.skipped)` after running the test in the same way as failures and errors are handled. If they are the same, the test isn't skipped.
### Testing
`python test/run_test.py -i test_autograd --verbose` to confirm that the disabled test `test_profiler_seq_nr` is run 50 times always in rerun mode
Pull Request resolved: https://github.com/pytorch/pytorch/pull/90888
Approved by: https://github.com/clee2000
