Show suggestion for "Local function can be made static" in IDE

[bkoelman]

Resharper: "Local function can be made static" is at warning level in cibuild, but was turned off in IDE. This fixes the mismatch reported at #1466 (comment).

We haven't used local functions much in the codebase before, which is why this mismatch went unnoticed until now.

QUALITY CHECKLIST

• N/A: Changes implemented in code
• Complies with our contributing guidelines
• N/A: Adapted tests
• N/A: Documentation updated

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (be6decc) 90.74% compared to head (3f50ce3) 90.74%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1473   +/-   ##
=======================================
  Coverage   90.74%   90.74%           
=======================================
  Files         344      344           
  Lines       11002    11002           
  Branches     1811     1804    -7     
=======================================
  Hits         9984     9984           
  Misses        669      669           
  Partials      349      349           

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