add a regression test

tests/crashes/128097.rs

@@ -1,6 +0,0 @@
-//@ known-bug: #128097
-#![feature(explicit_tail_calls)]
-fn f(x: &mut ()) {
-    let _y: String;
-    become f(x);
-}

tests/ui/explicit-tail-calls/two-phase.rs

@@ -0,0 +1,14 @@
+// regression test for <https://github.com/rust-lang/rust/issues/112788>.
+// this test used to ICE because we tried to run drop glue of `x`
+// if dropping `_y` (happening at the `become` site) panicked and caused an unwind.
+//
+//@ check-pass
+#![expect(incomplete_features)]
+#![feature(explicit_tail_calls)]
+
+fn f(x: &mut ()) {
+    let _y = String::new();
+    become f(x);
+}
+
+fn main() {}