Add a test for never type fallback edition change

Author: WaffleLapkin

tests/ui/editions/never-type-fallback.e2021.run.stdout

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+return type = ()

tests/ui/editions/never-type-fallback.e2024.run.stdout

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+return type = !

tests/ui/editions/never-type-fallback.rs

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+//@ revisions: e2021 e2024
+//
+//@[e2021] edition: 2021
+//@[e2024] edition: 2024
+//@[e2024] compile-flags: -Zunstable-options
+//
+//@ run-pass
+//@ check-run-results
+
+fn main() {
+    print_return_type_of(|| panic!());
+}
+
+fn print_return_type_of<R>(_: impl FnOnce() -> R) {
+    println!("return type = {}", std::any::type_name::<R>());
+}