Solve deprecations in t3olayout

In order to update typo3.org to v9 as smoothly as possible, all extensions it requires should support v9 properly.

TYPO3Scanner result for t3olayout:

Found 3 matches in 1.81s when checking for changes and deprecations in TYPO3 9

strong	weak	IMPORTANT
0.0% (0)	100.0% (3)	100.0% (3)

Classes/Domain/Finishers/GitlabFinisher.php
Fetch of property "response" (weak)
109 $result = json_decode($res->response, true);
Important: #83869 - Removed request type specific code in Bootstrap
https://docs.typo3.org/typo3cms/extensions/core/Changelog/9.2/Important-83869-RemovedRequestTypeSpecificCodeInBootstrap.html

Fetch of property "response" (weak)
116 $issue = json_decode($issue->response, true);
Important: #83869 - Removed request type specific code in Bootstrap
https://docs.typo3.org/typo3cms/extensions/core/Changelog/9.2/Important-83869-RemovedRequestTypeSpecificCodeInBootstrap.html

Classes/Services/ApiClientService.php
Fetch of property "response" (weak)
130 $client->response = curl_exec($client->handle);
Important: #83869 - Removed request type specific code in Bootstrap
https://docs.typo3.org/typo3cms/extensions/core/Changelog/9.2/Important-83869-RemovedRequestTypeSpecificCodeInBootstrap.html

These deprecations should either be solved in the update branch develop-v9 directly, or have a Merge Request pointed to that branch in the t3olayout repository.