fix pw setting for molecule in XPS calculation

[superstar54]

For molecules, we use gamma_only and assume_isolated. This should be fixed in the aiida-quantumespresso XpsWorkchain, but we don't want to wait for the new PR and release. Thus, we fix it here directly.

I also adjust the supercell_min_parameter_map, so it uses the default 8.0 when the user selects the moderate protocol.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 75.83%. Comparing base (f64607c) to head (bfecdef).

Files	Patch %	Lines
src/aiidalab_qe/plugins/xps/workchain.py	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #625      +/-   ##
==========================================
- Coverage   75.90%   75.83%   -0.08%     
==========================================
  Files          60       60              
  Lines        4291     4295       +4     
==========================================
  Hits         3257     3257              
- Misses       1034     1038       +4     

Flag	Coverage Δ
python-3.10	75.83% <0.00%> (-0.08%)	⬇️
python-3.8	75.86% <0.00%> (-0.08%)	⬇️
python-3.9	75.86% <0.00%> (-0.08%)	⬇️

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[PNOGillespie]

Looks fine to me and a quick test on my machine works with no issues. Good work @superstar54.