net-im/telegram-desktop: bump PORTREVISION after Qt5 was updated to 5.15.11p0 (+)

Some users report about startup coredumps with error meesage
"cannot mix incopatible Qt library (5.15.10) with this library (5.15.11)"
after installing new Qt5 packages from the repo.

Bump PORTREVISION to ensure users always get rebuilded package