fix: use-setstate-synchronously edge cases

[Desdaemon]

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

• Documentation update
• 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:

What changes did you make? (Give an overview)

Fixes mountedness invalidation in this case:

if (mounted) { // or 'while'
  await fetch();
}
setState(() {}); // LINT

Is there anything you'd like reviewers to focus on?

[Desdaemon]

Since this lint is yet to be released, should I still add this fix to the changelog?

[incendial]

@Desdaemon yeah, please add it to start the tests pipeline

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
No Duplication information

[codecov]

Codecov Report

Merging #1128 (676a198) into master (1630010) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1128      +/-   ##
==========================================
- Coverage   85.38%   85.37%   -0.01%     
==========================================
  Files         348      348              
  Lines        7743     7742       -1     
==========================================
- Hits         6611     6610       -1     
  Misses       1132     1132              

Impacted Files	Coverage Δ
...rules_list/use_setstate_synchronously/visitor.dart	93.10% <100.00%> (-0.12%)	⬇️

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