make-release: fix tag conversion of branch
Support for converting old branches to tag was introduced back in 2021 by c3f8dc8e for T250095. I ran it to delete the REL1_19 branch but but created tags pointing to the HEAD of the repository. The reason is the TagInfo that is put to the server must be passed using the "json" keyword argument.
I suspect we never ran the conversion. T250095 was aiming at removing
the wmf branches which we remove using scap clean (T303828).
This change will let us remove the old legacy REL* branches (T380841).
Edited by Hashar