upgrade to checkstyle 12.2.0

[romani]

https://checkstyle.org/releasenotes.html#Release_12.2.0

[romani]

@vtintillier , @Calixte , @Bananeweizen , fyi.

library project will migrate on jdk21 as minimal requirement jdk on January 2026. next release, in december 2026, most likely 12.3.0, will be last release before jdk21.

So in January 2026 we will release 13.0.0 (jdk21 as minimal jdk for runtime).