Diffusion - missed a "dont load diffusion request" in the code serving pathway

Summary: Fixes T6939.

Test Plan: From the task, visited a URI like http://code.example.com/diffusion/REPO/repo.git/info/refs?service=git-upload-pack. Before the patch, I got an error and post patch I get a nice login prompt to provide credentials to the repository, as expected based on my confguration

Reviewers: chad, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T6939

Differential Revision: https://secure.phabricator.com/D11348

src/applications/diffusion/controller/DiffusionServeController.php

@@ -2,6 +2,10 @@
 
 final class DiffusionServeController extends DiffusionController {
 
+  protected function shouldLoadDiffusionRequest() {
+    return false;
+  }
+
   public static function isVCSRequest(AphrontRequest $request) {
     if (!self::getCallsign($request)) {
       return null;