Rollup merge of #90304 - vandenheuvel:test_issue_75961, r=Mark-Simulacrum

Add regression test for #75961

Closes #75961.
Closes #21203.

src/test/ui/trait-bounds/issue-75961.rs

@@ -0,0 +1,7 @@
+// check-pass
+
+pub fn foo<'a>(s: &'a mut ()) where &'a mut (): Clone {
+    <&mut () as Clone>::clone(&s);
+}
+
+fn main() {}