Bug#1099164: pygobject: Don't include 3.51 with trixie

[Jeremy Bícha]

Someone tried pygobject 3.51.0-1 and complained that ibus-anthy
stopped working correctly for them at https://bugs.debian.org/1099192

It is unclear to me whether we have mispackaged pygobject 3.52 or
whether someone needs to fix a lot of other packages. I haven't really
looked into this issue yet since we won't be using pygobject 3.52 for
Debian 13 or for Ubuntu 25.04.

Thank you,
Jeremy Bícha