Bug#997415: build depends on tex-gyre

[Andrius Merkys]

Control: tags -1 + patch

Hello,

This issue should be fixed by build-depending on tex-gyre which provides
the missing tgtermes.sty. I have successfully built
gprbuild-2021.0.0.0778b109 in clean chroot with tex-gyre additionally
installed.

Andrius