Accept also linked worktree directories
Directories that contain a linked worktree don't have a .git
folder, but a .git
file which contains the route to the
worktree info in the original repository.
Git commands do still work as usual on this directories, so
just expanding the check for a .git
file makes kdesrc-build
work on a git worktree link of the repo.
This helps to have a dual set-up (kf5/kf6) with a different source path for different build groups and branches (eg kf5/master) using git worktree
instead of full cloned repos.