fix(test): remove period in test_flatten_grammar_with_recursive_inline_variable

The period was dropped in the `thiserror` refactor
(79444e07f9), which caused the
`test_flatten_grammar_with_recursive_inline_variable` test to fail.

Signed-off-by: James McCoy <jamessan@jamessan.com>
(cherry picked from commit a6e530b33d)

cli/generate/src/prepare_grammar/flatten_grammar.rs

@@ -533,7 +533,7 @@ mod tests {
 
         assert_eq!(
             result.unwrap_err().to_string(),
-            "Rule `test` cannot be inlined because it contains a reference to itself.",
+            "Rule `test` cannot be inlined because it contains a reference to itself",
         );
     }
 }