use dump-solver-proof-tree in a test

Author: BoxyUwU

tests/ui/traits/new-solver/alias_eq_simple.rs

@@ -1,5 +1,12 @@
 // check-pass
 // compile-flags: -Ztrait-solver=next
+// compile-flags: -Zdump-solver-proof-tree=always
+// compile-flags: -Zdump-solver-proof-tree-use-cache=no
+
+#![feature(rustc_attrs)]
+#![rustc_filter_proof_tree_dump(
+    "Binder { value: TraitPredicate(<(i32, u32) as TraitA>, polarity:Positive), bound_vars: [] }"
+)]
 
 // test that the new solver can handle `alias-eq(<i32 as TraitB>::Assoc, u32)`