chore(tests): Cleanup bootstrap.php to be forward-compatible

[come-nc]

This uses the new tests/autoload.php from nextcloud/server instead of messing directly with OC private autoloader.

See nextcloud/server#52951 and nextcloud/server#52945 for context.

[come-nc]

CI failure is unrelated and should be fixed first before rebasing this PR.
Most likely a dependency update missing?

PHP Fatal error:  Uncaught Behat\Testwork\Call\Exception\CallErrorException: 8192: Symfony\Component\String\UnicodeString::join(): Implicitly marking parameter $lastGlue as nullable is deprecated, the explicit nullable type must be used instead in /home/runner/actions-runner/_work/limit_login_to_ip/limit_login_to_ip/apps/limit_login_to_ip/tests/integration/vendor/symfony/string/UnicodeString.php line 179 in /home/runner/actions-runner/_work/limit_login_to_ip/limit_login_to_ip/apps/limit_login_to_ip/tests/integration/vendor/behat/behat/src/Behat/Testwork/Call/Handler/RuntimeCallHandler.php:90
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