Proactively update coroutine drop shim's phase to account for later passes applied during shim query

tests/ui/async-await/post-cleanup-phase-validation.rs

@@ -0,0 +1,19 @@
+//@ compile-flags: -Zvalidate-mir
+//@ edition: 2024
+//@ build-pass
+
+// Regression test that we don't ICE when encountering a transmute in a coroutine's
+// drop shim body, which is conceptually in the Runtime phase but wasn't having the
+// phase updated b/c the pass manager neither optimizes nor updates the phase for
+// drop shim bodies.
+
+struct HasDrop;
+impl Drop for HasDrop {
+    fn drop(&mut self) {}
+}
+
+fn main() {
+    async {
+        vec![async { HasDrop }.await];
+    };
+}