B906 checks all classes, not just AST visitors

I'm seeing some false-positives from B906 where we have node visitors that are not using the stdlib ast library:

import libcst


class CSTVisitor(libcst.CSTVisitor):
    def visit_ClassDef(self, node):
        pass

$ flake8 --select=B906 t.py
t.py:5:5: B906 `visit_` function with no further calls to a visit function, which might prevent the `ast` visitor from properly visiting all nodes. Consider adding a call to `self.generic_visit(node)`.

In this case, libcst.CSTVisitor does not have a generic_visit method (and the error message explicitly talks about ast, which is confusing).

Should this rule make sure it only applies to ast visitors rather than other classes that have a visit_ method?

Start by reproducing B906 with the provided libcst.CSTVisitor example and the flake8 --select=B906 t.py command. Trace the B906 rule and its tests to determine how visitor classes are identified. Done means non-stdlib AST visitors are not incorrectly reported, while genuine AST visitor cases retain the intended diagnostic.