I believe it's true that the tag can be deleted or changed, which could cause problems with reproducability. I changed the above URL to use the hash of the commit and that gives the same results but with the guarantee of being reproducible. For the sake of documentation, here's the updated lines from the .spec:

%global owner michaeljones
%global commit0 aa95a879dccd63cfac5156bd9a303d41ea1d2490

Name:           breathe
Source0:        https://github.com/%{owner}/%{name}/archive/%{name}-%{commit0}.tar.gz

%setup -qn %{name}-%{commit0}