fix error message typo (apache#17570)

Author: AdamGS

datafusion/sql/src/expr/substring.rs

@@ -79,6 +79,7 @@ impl<S: ContextProvider> SqlToRel<'_, S> {
             }
         }
 
-        not_impl_err!("Substring could not be planned by registered expr planner. Hint: enable the `unicode_expressions" )
+        not_impl_err!("Substring could not be planned by registered expr planner. \
+                        Hint: Please try with `unicode_expressions` DataFusion feature enabled")
     }
 }

datafusion/sql/tests/sql_integration.rs

@@ -4633,7 +4633,7 @@ fn test_no_substring_registered() {
 
     assert_snapshot!(
         err.strip_backtrace(),
-        @"This feature is not implemented: Substring could not be planned by registered expr planner. Hint: enable the `unicode_expressions"
+        @"This feature is not implemented: Substring could not be planned by registered expr planner. Hint: Please try with `unicode_expressions` DataFusion feature enabled"
     );
 }
 
@@ -4645,7 +4645,7 @@ fn test_no_substring_registered_alt_syntax() {
 
     assert_snapshot!(
         err.strip_backtrace(),
-        @"This feature is not implemented: Substring could not be planned by registered expr planner. Hint: enable the `unicode_expressions"
+        @"This feature is not implemented: Substring could not be planned by registered expr planner. Hint: Please try with `unicode_expressions` DataFusion feature enabled"
     );
 }