gedit should switch tabs with Ctrl-PgUp and Ctrl-PgDown to be consistent with other apps

Gedit uses Ctrl-Alt-PgUp/PgDown for tab switching when others just use Ctrl-PgUp/PgDown. That's what gedit should use to be consistent with for example gnome-terminal and firefox. It also makes sense that Ctrl-Alt is reserved for more global actions like workspace switching

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: gedit 3.28.1-1ubuntu1
ProcVersionSignature: Ubuntu 4.15.0-29.31-generic 4.15.18
Uname: Linux 4.15.0-29-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.2
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Wed Aug 8 16:35:32 2018
InstallationDate: Installed on 2018-05-31 (69 days ago)
InstallationMedia: Ubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
SourcePackage: gedit
UpgradeStatus: No upgrade log present (probably fresh install)