Add test case for rust-lang#74256

Author: eholk

src/test/ui/async-await/issue-74256.rs

@@ -0,0 +1,15 @@
+// edition:2018
+
+struct Struct { }
+
+impl Struct {
+    async fn async_fn(self: &Struct, f: &u32) -> &u32 {
+        f
+    }
+
+    fn sync_fn(self: &Struct, f: &u32) -> &u32 {
+        f
+    }
+}
+
+fn main() {}