Add CI coverage for more filesystems

[samuelkarp]

Currently, we test the default filesystems in the GitHub Actions runners for a few operating systems:

continuity/.github/workflows/ci.yml

Line 45 in 72c70fe

os: [ubuntu-22.04, macos-12, windows-2019, windows-2022]

On Linux, this is just ext4. We should add coverage for additional filesystems such as xfs, btrfs, and zfs on Linux. We may also want to add coverage for filesystem options such as APFS with case-sensitivity on Mac OS.

#172 (comment) records some previous manual results on FreeBSD.