Don't run the new test against the GCC backend as it does not support become tail calls

Author: jakubadamw

tests/ui/explicit-tail-calls/default-trait-method.rs

@@ -3,6 +3,7 @@
 // in a path determining whether the method in question is marked as `#[track_caller]`.
 //
 //@ run-pass
+//@ ignore-backends: gcc
 
 #![feature(explicit_tail_calls)]
 #![expect(incomplete_features)]