Fix lazy loading bash_completion from XDG_DATA_DIRS
Fix lazy loading bash_completion from XDG_DATA_DIRS

If a bash_completion file should get lazy loaded and is placed in a none standard directory which is listed in XDG_DATA_DIRS it must be placed under share/bash-completion/completions. This is for example used in home-manager.

See https://github.com/scop/bash-completion/blob/730368b35aeb7f9b7eec62ff0e19b1bd8b385961/bash_completion#L2531
tj/git-extras,spacewander/git-extras