Add a test for pattern matching within a tuple

Author: Mark-Simulacrum

src/test/ui/issues/issue-74954.rs

@@ -0,0 +1,7 @@
+// check-pass
+
+fn main() {
+    if let Some([b'@', filename @ ..]) = Some(b"@abc123") {
+        println!("filename {:?}", filename);
+    }
+}