Problem matchers with multiple severities don't match every result

Describe the bug

If a problem matcher matches both errors and warnings and a build log contains mixed results not every result gets matched. Files with only errors or only warnings are matched correctly, but files with mixed results have only the first severity matched until the other severity is hit.

I ran into this while trying to add warning support to my Stylelint problem matcher action.

To Reproduce

Steps to reproduce the behavior:

1. Register a problem matcher with two matchers, one with an error severity and one with a warning severity
2. Emit both errors and warnings to the build log
3. Not all results will be matched

Expected behavior

For every error and warning to be matched, even when both are in the same file's results.

Runner Version and Platform

Version of your runner? 2.290.1

OS of the machine running the runner? all

What's not working?

Not all matched build log lines are being highlighted.

Job Log Output

Sample repo showing the issue https://github.com/xt0rted-test/problem-matcher-test/actions/runs/2248762840

Start with the linked sample repository and job log, then trace the runner's problem matcher handling for results with error and warning severities. Done means every error and warning in a mixed-severity build log is highlighted, including results from the same file.