invariant_booleans false positive with unary operations.

[dikmax]

Consider this code:

if (offset >= length) {
  return;
}

offset++;
if (offset >= length) { // Got error here.
}

With += works fine.

Linter 0.1.29

[dikmax]

As mentioned #57396, I can be sure that it reproducible in 0.1.27 (version bundled with Dart 1.20.1), not in 0.1.29.

[alexeieleusis]

This is indeed a bug, those operators were not considered when looking for mutations, this rule needs some cleanup, I will fix this bug after that. It will take a while, but will be fixed.