Fix flaky test_mount_unmount_zfs_file_system()

[pem70]

What It Does
Fixes #383

How to Test
Run test_mount_unmount_zfs_file_system() and make it fail before unmounting. The created file system should still be unmounted and deleted.

Review Checklist
I certify that I have:

• tested my changes
• added/updated automated tests
• updated the changelog
• followed the contribution guidelines

Additional Comments

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.88%. Comparing base (8fe22c2) to head (eeb463e).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #384   +/-   ##
=======================================
  Coverage   81.88%   81.88%           
=======================================
  Files          48       48           
  Lines        2771     2771           
=======================================
  Hits         2269     2269           
  Misses        502      502           

Flag	Coverage Δ
unittests	81.88% <ø> (ø)

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[zFernand0]

Shifting things a bit in the GH project. However, this is still in my radar to review 🙏