Fix issue followed PEP-8 standard

[stevenhua0320]

Leave 2 F401 error in formalletterbu…ilder.py in try statement with import modules.

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 67.86%. Comparing base (9fb62aa) to head (83b04df).
Report is 67 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1083      +/-   ##
==========================================
- Coverage   68.20%   67.86%   -0.35%     
==========================================
  Files          77       79       +2     
  Lines        8576     8622      +46     
==========================================
+ Hits         5849     5851       +2     
- Misses       2727     2771      +44     

Files	Coverage Δ
regolith/builders/beamplanbuilder.py	95.23% <ø> (ø)
regolith/builders/cpbuilder.py	97.26% <100.00%> (-0.04%)	⬇️
regolith/builders/figurebuilder.py	45.45% <ø> (+1.97%)	⬆️
regolith/builders/formalletterbuilder.py	80.00% <100.00%> (-0.60%)	⬇️
regolith/builders/coabuilder.py	44.84% <0.00%> (ø)

... and 6 files with indirect coverage changes

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