test_runner: correct "already mocked" error punctuation placement

PR-URL: https://github.com/nodejs/node/pull/58840
Reviewed-By: Pietro Marchini <pietro.marchini94@gmail.com>
Reviewed-By: Ethan Arrowood <ethan@arrowood.dev>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

lib/internal/test_runner/mock/mock.js

@@ -671,7 +671,7 @@ class MockTracker {
 
     if (baseURL.searchParams.has(kMockSearchParam)) {
       throw new ERR_INVALID_STATE(
-        `Cannot mock '${specifier}.' The module is already mocked.`,
+        `Cannot mock '${specifier}'. The module is already mocked.`,
       );
     }