Fix flaky test

[jenshnielsen]

In pyvisa 1.16 an additional warning may be triggered during shutdown if the resource is already closed.
Rewrite test to not depend on the exact number of warnings logged

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.89%. Comparing base (7f0af7e) to head (4f129cc).
⚠️ Report is 22 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7768   +/-   ##
=======================================
  Coverage   59.89%   59.89%           
=======================================
  Files         352      352           
  Lines       31807    31806    -1     
=======================================
  Hits        19051    19051           
+ Misses      12756    12755    -1     

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