Add regression test for #55976

Signed-off-by: Yuki Okushi <jtitor@2k36.org>

src/test/ui/codegen/issue-55976.rs

@@ -0,0 +1,13 @@
+// run-pass
+// ^-- The above is needed as this issue is related to LLVM/codegen.
+// min-llvm-version:15.0.0
+// ^-- The above is needed as this issue is fixed by the opaque pointers.
+
+fn main() {
+    type_error(|x| &x);
+}
+
+fn type_error<T>(
+    _selector: for<'a> fn(&'a Vec<Box<dyn for<'b> Fn(&'b u8)>>) -> &'a Vec<Box<dyn Fn(T)>>,
+) {
+}