Bug#1148616: Raising severity of GNOME Shell 51 extensions bugs

[Jeremy Bícha]

Control: severity -1 serious

We'll be requesting approval from the Debian Release Team soon to do
the GNOME Shell 51 transition. Therefore, I'm raising the severity of
these bugs. Packages that aren't ready by the time GNOME Shell 51 is
ready to migrate to Testing will be removed from Testing to complete
the transition.

Thank you,
Jeremy Bícha