Remove accidental stray parenthesis in new codejam rule

Co-authored-by: Kieran Siek <[email protected]>

Author: Bluenix2

pydis_site/templates/events/pages/code-jams/9/rules.html

@@ -18,7 +18,7 @@
         <p>
             Exceptions to this rule are made for resources such as databases and files, albeit excluding usage other than for storage.
             For example, you may use PostgreSQL as a database but not its `NOTIFY` command.
-            Lastly, working with subprocesses (through stdin/stdout or <code>multiprocessing.Pool()</code>/<code>concurrent.futures.ProcessPoolExecutor()(</code>) is also exempted from this rule.
+            Lastly, working with subprocesses (through stdin/stdout or <code>multiprocessing.Pool()</code>/<code>concurrent.futures.ProcessPoolExecutor()</code>) is also exempted from this rule.
         </p>
     </li>
     <li><p>Your solution should be platform agnostic. For example, if you use filepaths in your submission, use <code>pathlib</code> to create platform agnostic Path objects instead of hardcoding the paths.</p></li>