There is special code in the CI to handle the submodules of the VisualEditor Mediawiki extension. We should generalize that for all extensions or make VisualEditor stop using submodules.
This task was created after: https://gerrit.wikimedia.org/r/#/c/262432/
See also: T51846
List of potentially affected extensions:
$ cd projects/mediawiki/extensions $ ls -1 */.gitmodules|cut -d\/ -f1