Add a test to the gitaly data_dirs recipe for symbols
This tests that we have maintained support for users using symbols as their keys instad of strings, this can end up happening when they specify something like:
git_data_dirs({'default': {'path': '/some/path'})
Where the :
(colon) syntax results in the keys being symbols rather
than strings.
We had a recent regression related to this that was fixed in: !2303 (merged)