feat(pull-request): add update-branch endpoint

lib/Github/Api/PullRequest.php

@@ -177,6 +177,23 @@ public function update($username, $repository, $id, array $params)
         return $this->patch('/repos/'.rawurlencode($username).'/'.rawurlencode($repository).'/pulls/'.rawurlencode($id), $params);
     }
 
+    /**
+     * Update a pull request branch with the latest changes from its base branch.
+     *
+     * @link https://docs.github.com/en/rest/pulls/pulls#update-a-pull-request-branch
+     *
+     * @param string $username   the username
+     * @param string $repository the repository
+     * @param string $id         the ID of the pull request whose branch should be updated
+     * @param array  $params     Optional request parameters such as expected_head_sha
+     *
+     * @return array|string
+     */
+    public function updateBranch($username, $repository, $id, array $params = [])
+    {
+        return $this->put('/repos/'.rawurlencode($username).'/'.rawurlencode($repository).'/pulls/'.rawurlencode($id).'/update-branch', $params);
+    }
+
     public function merged($username, $repository, $id)
     {
         return $this->get('/repos/'.rawurlencode($username).'/'.rawurlencode($repository).'/pulls/'.rawurlencode($id).'/merge');

test/Github/Tests/Api/PullRequestTest.php

@@ -173,6 +173,23 @@ public function shouldUpdatePullRequests()
         $this->assertEquals($expectedArray, $api->update('ezsystems', 'ezpublish', 15, ['state' => 'aa', 'some' => 'param']));
     }
 
+    /**
+     * @test
+     */
+    public function shouldUpdatePullRequestBranch()
+    {
+        $expectedArray = ['message' => 'Update request accepted'];
+        $params = ['expected_head_sha' => str_repeat('A', 40)];
+
+        $api = $this->getApiMock();
+        $api->expects($this->once())
+            ->method('put')
+            ->with('/repos/ezsystems/ezpublish/pulls/15/update-branch', $params)
+            ->willReturn($expectedArray);
+
+        $this->assertSame($expectedArray, $api->updateBranch('ezsystems', 'ezpublish', 15, $params));
+    }
+
     /**
      * @test
      */