Amend fix: type call error for AiiDAConfigDir.set

[unkcpz]

One place not use the correct type cast for config path passing to AiiDAConfigDir.set after #6610

[unkcpz]

Thanks @mbercx! Here is a quick amend fix. I also did a search globally and this is the only place I didn't use the correct type casting for path string (hopefully).
I was trying to add a test for the fixture, but the code path where error raised is hard to mock (it require first the reset and then the config fixture yield failed), so I gave up.

[unkcpz]

I think this fixture is deprecated, it is better to use the one in aiida/tools/pytest_fixtures. But for not breaking also other plugins that use the old fixture, this fix is required.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 77.89%. Comparing base (ef60b66) to head (b27abf2).
Report is 151 commits behind head on main.

Files with missing lines	Patch %	Lines
src/aiida/manage/tests/pytest_fixtures.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6646      +/-   ##
==========================================
+ Coverage   77.51%   77.89%   +0.39%     
==========================================
  Files         560      567       +7     
  Lines       41444    42180     +736     
==========================================
+ Hits        32120    32853     +733     
- Misses       9324     9327       +3     

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[unkcpz]

I just merge this without approve since it is a fix for deprecated API and this should fix nightly test fail in aiida-quantumespresso.