fix: set preview header for endpoints that require it only

Author: iBotPeaches

lib/Github/Api/Repository/Protection.php

@@ -34,6 +34,9 @@ public function configure()
      */
     public function show($username, $repository, $branch)
     {
+        // Preview endpoint
+        $this->acceptHeaderValue = 'application/vnd.github.luke-cage-preview+json';
+
         return $this->get('/repos/'.rawurlencode($username).'/'.rawurlencode($repository).'/branches/'.rawurlencode($branch).'/protection');
     }
 
@@ -51,6 +54,9 @@ public function show($username, $repository, $branch)
      */
     public function update($username, $repository, $branch, array $params = [])
     {
+        // Preview endpoint
+        $this->acceptHeaderValue = 'application/vnd.github.luke-cage-preview+json';
+
         return $this->put('/repos/'.rawurlencode($username).'/'.rawurlencode($repository).'/branches/'.rawurlencode($branch).'/protection', $params);
     }