Bugfix 1182: Unskip test that is no longer flaky

[alexowens90]

Closes #1182

Git archaeology suggests this test has not been flaky for a while, and that it was mistakenly skipped, Evidence:

• Original bullet point in flaky tests epic linked to (now expired) logs from a build on 14/7/23, which had an old implementation of this test, and said that the failure looked similar to test_read_ts, which also had an old implementation using sleeps instead of the distinct_timestamps context manager now in use in both tests on master
• The distinct_timestamps context manager was added to test_find_version in a PR on 10/8/23, and the test was not marked as skipped at this point.
• The xfail mark was added in a commit titled "Reapply parts of the previous commit that isn't superseded without formatting to avoid conflicts", merged as part of this PR.
• However, none of the other commits in this PR removed the xfail, suggesting only the changes to test_file_config.py were intentional.

For additional safety, I ran the test 1000 times in all supported configurations in the CI, with no failures.