gitstats: Added more tags to the generated test repo
This makes it easier to refer to tags instead of hashes in
the test cases. This is a major advantage when the hashes
change, as it means that only the expected output of the
tests will have to be changed. Currently, the changed hash
has to be looked up in the old version, and then the commit
that it refers to found in the new version, which hash may
then be used. This eliminates that need, and will make such
a hash change a lot easier to correct.