Revert "Delete broken #[deprecated] test"

This reverts commit 8862629bcc.

tests/test_deprecated.rs

@@ -0,0 +1,10 @@
+#![deny(deprecated, clippy::all, clippy::pedantic)]
+
+use thiserror::Error;
+
+#[derive(Error, Debug)]
+pub enum Error {
+    #[deprecated]
+    #[error("...")]
+    Deprecated,
+}