[phpunit] skip variable-callable in NoAssertFuncCallInTestsRule

[TomasVotruba]

Problem

NoAssertFuncCallInTestsRule targets the assert() language construct in test classes. But NamingHelper::getName() also resolves Variable nodes, so an invoked variable-callable named $assert was flagged too:

public function testMe(callable $assert)
{
    $assert(100); // false positive
}

Fix

Require $node->name instanceof Name before name check, so only real function/construct calls match. Variable-callables are skipped. Added a skip fixture.