Fix linter complaints

[nightwing]

fixes #5732 #5733
code coverage complain can be ignored, since that part is disabled in test runner

[codecov]

Codecov Report

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

Project coverage is 87.05%. Comparing base (6f05b92) to head (71c3ae2).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
src/mode/_test/highlight_rules_test.js	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5735      +/-   ##
==========================================
- Coverage   87.06%   87.05%   -0.01%     
==========================================
  Files         598      598              
  Lines       43713    43714       +1     
  Branches     7164     7164              
==========================================
  Hits        38057    38057              
- Misses       5656     5657       +1     

Flag	Coverage Δ
unittests	87.05% <0.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.