freebsd.yml, GnuTests.yml: Use ubuntu-latest as VM's glibc is used

[oech3]

No benefit to pin runner since they use VM provided glibc (manual updating is annoying).
Closes #14667 .

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/df/skip-rootfs. tests/df/skip-rootfs is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/id/smack. tests/id/smack is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/mkdir/smack-root. tests/mkdir/smack-root is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/printf/printf. tests/printf/printf is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/seq/seq-precision. tests/seq/seq-precision is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/shuf/shuf. tests/shuf/shuf is passing on 'main'. Maybe you have to rebase?
Note: The gnu test tests/misc/getopt_vs_usage was skipped on 'main' but is now failing.
Note: The gnu test tests/misc/usage_vs_refs was skipped on 'main' but is now failing.