Ensure UNK* files are passed to Wannier90 when plotting Wannier functions

[elinscott]

Closes #246

[codecov]

Codecov Report

Attention: Patch coverage is 40.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 80.67%. Comparing base (d980150) to head (57dc5c8).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
src/koopmans/workflows/_wannierize.py	40.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #248      +/-   ##
==========================================
- Coverage   80.69%   80.67%   -0.03%     
==========================================
  Files          97       97              
  Lines        8186     8191       +5     
==========================================
+ Hits         6606     6608       +2     
- Misses       1580     1583       +3     

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