tests: allow age to go up to triple digits in test-shelve.t
We started to glob the age of shelved changes in 51934fc796c0, which says that
sometimes tests run slow and hg shelve --list says "2s" instead of "1s".
However in some instances, like , tests run so slow that the age goes up to
double digits ("13s" in that case). When that happens, hg shelve --list
output has less white spaces after the age, so let's glob the spaces too. We
probably won't ever need to handle triple digits there, but I went ahead and
left only 2 required white spaces in total.