Add a test demonstrating that RFC's note on diverging returns is subsumed by just inferring unit as ret type

Author: compiler-errors

tests/ui/coroutine/return-types-diverge.rs

@@ -0,0 +1,18 @@
+// compile-flags: --edition 2024 -Zunstable-options
+// check-pass
+
+#![feature(gen_blocks)]
+
+async gen fn async_gen_fn() -> i32 { return }
+
+gen fn gen_fn() -> i32 { return }
+
+fn async_gen_block() {
+    async gen { yield (); return };
+}
+
+fn gen_block() {
+    gen { yield (); return };
+}
+
+fn main() {}