bug #1030 Add accept header for creating repo from template (davidpeach)

This PR was squashed before being merged into the 3.4.x-dev branch.

Discussion
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This still requires an accept header as per the docs: https://docs.github.com/en/rest/reference/repos#create-a-repository-using-a-template-preview-notices

Commits
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34e3370 Add accept header for creating repo from template
91b3911 Update Repo.php

Author: davidpeach

lib/Github/Api/Repo.php

@@ -805,6 +805,9 @@ public function transfer($username, $repository, $newOwner, $teamId = [])
      */
     public function createFromTemplate(string $templateOwner, string $templateRepo, array $parameters = [])
     {
+        //This api is in preview mode, so set the correct accept-header
+        $this->acceptHeaderValue = 'application/vnd.github.baptiste-preview+json';
+
         return $this->post('/repos/'.rawurldecode($templateOwner).'/'.rawurldecode($templateRepo).'/generate', $parameters);
     }
 }