Fix tests on MW 38

[JeroenDeDauw]

1. Maps\Tests\Integration\DataAccess\GeoJsonFetcherTest::testWhenFileRetrievalFails_emptyJsonIsReturned
   LogicException: This ParserOutput contains no text!
   /home/runner/work/Maps/Maps/mediawiki/includes/parser/ParserOutput.php:363
   /home/runner/work/Maps/Maps/mediawiki/extensions/Maps/src/Presentation/OutputFacade.php:33
   /home/runner/work/Maps/Maps/mediawiki/extensions/Maps/src/GeoJsonPages/GeoJsonMapPageUi.php:23
   /home/runner/work/Maps/Maps/mediawiki/extensions/Maps/src/GeoJsonPages/GeoJsonContent.php:62
   /home/runner/work/Maps/Maps/mediawiki/extensions/Maps/src/GeoJsonPages/GeoJsonContent.php:56