In commit cd377f45c9 (refs: loosen restriction on wildcard "*"
refspecs, 2015-07-22) in git.git, the restrictions on wildcard
"*" refspecs has been loosened. While wildcards were previously
only allowed if the component is a single "*", this was changed
to also accept other patterns as part of the component.

We never adapted to that change and still reject any wildcard
patterns that aren't a single "*" only. Update our tests to
reflect the upstream change and adjust our own code accordingly.