tests linux: do not skip tests depending on kernel <= 6.11

[Marcondiro]

Description

The Linux images used in CI are on 6.11 at the time of writing. Remove the test requiring a kernel <= 6.11 from the skipped ones, addressing the FIXMEs.

Sources

Checklist

• Relevant tests in libc-test/semver have been updated
• No placeholder or unstable values like *LAST or *MAX are
  included (see #3131)
• Tested locally (cd libc-test && cargo test --target mytarget);
  especially relevant for platforms that may not be checked in CI

[tgross35]

I think we're stuck to the host (ubuntu-24.04) kernel versions here since Docker doesn't bring its own kernel. Per https://en.wikipedia.org/wiki/Ubuntu_version_history#Table_of_versions that means 6.8.