Allow multiple paths in GIT_SUBMODULE_PATHS
What does this MR do?
As discussed in !2249 (comment 619585733) and #27233 (closed) hereby trying to fix GIT_SUBMODULE_PATHS to be compatible with multiple submodule selection/exclusion.
Why was this MR needed?
Though !2249 (merged) described GIT_SUBMODULE_PATHS to be able to selected/exclude multiple submodules in practice it was not possible to do so since gitlab-runner was adding single quotes around the pathspec resulting in GIT seeing the list of paths as a single pathspec.
What's the best way to test this MR?
Create a GIT project with more than 1 submodule and try selecting/excluding 2 or more of them via GIT_SUBMODULE_PATHS yaml variable.