fix: remove duplicated highlights and ignore void function calls

[incendial]

What is the purpose of this pull request? (put an "X" next to an item)

[ ] Documentation update
[X] Bug fix
[ ] New rule
[ ] Changes an existing rule
[ ] Add autofixing to a rule
[ ] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

[github-actions]

Dart Code Metrics unused files report of dart_code_metrics. ✅

Summary

• Scanned package folders: bin, example, lib
• No unused files found! ✅

[github-actions]

Dart Code Metrics analyze report of dart_code_metrics. ✅

Summary

• Scanned folders: bin, example, lib, test

• Total scanned files: 424

• Total lines of source code: 7448

• Total classes: 290

• Average Cyclomatic Number per line of code: 0.35

• Average Source Lines of Code per method: 6

• Total tech debt: 1310.0 hours

• Found issues: 6 ⚠

[codecov]

Codecov Report

Merging #829 (b532ffa) into master (20a82cc) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #829   +/-   ##
=======================================
  Coverage   87.32%   87.32%           
=======================================
  Files         279      279           
  Lines        5932     5934    +2     
=======================================
+ Hits         5180     5182    +2     
  Misses        752      752           

Impacted Files	Coverage Δ
.../rules_list/prefer_moving_to_variable/visitor.dart	100.00% <100.00%> (ø)

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