MissingTypehintCheck: reduce duplicate work

[staabm]

after PR

➜  phpstan-src git:(2.1.x) ✗ hyperfine 'php bin/phpstan analyze bug-12661.php --debug' -i
Benchmark 1: php bin/phpstan analyze bug-12661.php --debug
  Time (mean ± σ):      1.059 s ±  0.005 s    [User: 0.953 s, System: 0.102 s]
  Range (min … max):    1.053 s …  1.068 s    10 runs
 
  Warning: Ignoring non-zero exit code.
 

before this PR

➜  phpstan-src git:(2.1.x) ✗ hyperfine 'php bin/phpstan analyze bug-12661.php --debug' -i
Benchmark 1: php bin/phpstan analyze bug-12661.php --debug
  Time (mean ± σ):      1.111 s ±  0.019 s    [User: 0.993 s, System: 0.115 s]
  Range (min … max):    1.083 s …  1.151 s    10 runs
 
  Warning: Ignoring non-zero exit code.

on the reproducer of phpstan/phpstan#12661

[phpstan-bot]

This pull request has been marked as ready for review.

[ondrejmirtes]

Thank you.