add syntax validation test for &impl 'a

Author: Shourya742

crates/syntax/test_data/parser/validation/impl_trait_lifetime_only.rast

@@ -0,0 +1,29 @@
+[email protected]
+  [email protected]
+    [email protected] "fn"
+    [email protected] " "
+    [email protected]
+      [email protected] "f"
+    [email protected]
+      [email protected] "("
+      [email protected]
+        [email protected]
+          [email protected] "_"
+        [email protected] ":"
+        [email protected] " "
+        [email protected]
+          [email protected] "&"
+          [email protected]
+            [email protected] "impl"
+            [email protected] " "
+            [email protected]
+              [email protected]
+                [email protected]
+                  [email protected] "'a"
+      [email protected] ")"
+    [email protected] " "
+    [email protected]
+      [email protected]
+        [email protected] "{"
+        [email protected] "}"
+error 9..16: At least one trait must be specified

crates/syntax/test_data/parser/validation/impl_trait_lifetime_only.rs

@@ -0,0 +1 @@
+fn f(_: &impl 'a) {}