Fix record cache test

[Schamper]

The test was unnecessarily restrictive towards zstandard filenames. This is not needed. This now showed up because we merged #1380, which removes the zstandard dependency. And because we pinned to an older version of flow.record, it now won't use zstandard files as default.

When we update the flow.record dependency to fox-it/flow.record#198, all will be righteous again.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.00%. Comparing base (52e9f84) to head (a602e23).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1441   +/-   ##
=======================================
  Coverage   81.00%   81.00%           
=======================================
  Files         376      376           
  Lines       33649    33649           
=======================================
  Hits        27256    27256           
  Misses       6393     6393           

Flag	Coverage Δ
unittests	81.00% <ø> (ø)

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[codspeed-hq]

CodSpeed Performance Report

Merging #1441 will not alter performance

_{Comparing fix-record-cache-test (a602e23) with main (52e9f84)}

Summary

✅ 9 untouched