Fix incomplete requireRootInDeclaration check in InvalidPackageDeclaration

[cketti]

The old code used String.startsWith() to check if the package declaration is the root package or a subpackage of it. This check erroneously allows "sibling packages" that start with the root package name, e.g. "com.example_extra" when the root package name is "com.example".

This PR adds a test for that case and fixes the check to work as intended.

[codecov]

Codecov Report

Merging #6045 (a595db9) into main (42a48d5) will decrease coverage by 0.01%.
The diff coverage is 82.35%.

@@             Coverage Diff              @@
##               main    #6045      +/-   ##
============================================
- Coverage     84.84%   84.83%   -0.01%     
- Complexity     3944     3946       +2     
============================================
  Files           561      561              
  Lines         13251    13256       +5     
  Branches       2313     2314       +1     
============================================
+ Hits          11243    11246       +3     
- Misses          868      869       +1     
- Partials       1140     1141       +1     

Impacted Files	Coverage Δ
...h/detekt/rules/naming/InvalidPackageDeclaration.kt	91.89% <82.35%> (-4.99%)	⬇️

[cortinico]

Nice catch 👍 Thanks for the fix @cketti