hcoles/pitest#1440 is fixed

We need to revert this suppression
https://github.com/checkstyle/checkstyle/pull/18443/changes#diff-9c5fb3d1b7e3b0f54bc5c4182965c4fe1f9023d449017cece3005d3f90e8e4d8L5008

If issue fixes fully, no other changes will be required.
If there some mutation CI find, we should report it to pitest project

Scope becomes a bit bigger, we have 4 more case with such suppression in pom.xml:

<!-- Disabled until issue in pitest is resolved at https://github.com/hcoles/pitest/issues/1440 -->
<!-- <mutator>EXPERIMENTAL_MEMBER_VARIABLE</mutator> -->
                

We need to uncomment this mutator.