Add a regression test for unsafe nonexistent attributes

Author: JonathanBrouwer

tests/ui/attributes/unsafe/unsafe-nonexistent-attribute.rs

@@ -0,0 +1,10 @@
+// This is a regression test for https://github.com/rust-lang/rust/issues/148453
+// We want the `cannot find attribute` error to appear before `is not an unsafe attribute`
+//@ edition: 2024
+
+#[unsafe(does_not_exist)]
+//~^ ERROR cannot find attribute
+//~| ERROR is not an unsafe attribute
+fn aa() {}
+
+fn main() {}

tests/ui/attributes/unsafe/unsafe-nonexistent-attribute.stderr

@@ -0,0 +1,16 @@
+error: cannot find attribute `does_not_exist` in this scope
+  --> $DIR/unsafe-nonexistent-attribute.rs:5:10
+   |
+LL | #[unsafe(does_not_exist)]
+   |          ^^^^^^^^^^^^^^
+
+error: `does_not_exist` is not an unsafe attribute
+  --> $DIR/unsafe-nonexistent-attribute.rs:5:3
+   |
+LL | #[unsafe(does_not_exist)]
+   |   ^^^^^^ this is not an unsafe attribute
+   |
+   = note: extraneous unsafe is not allowed in attributes
+
+error: aborting due to 2 previous errors
+