Unable to scroll tabs by mouse wheel in Pluma's Side Pane

[Norbert]

#### Expected behaviour
In previous MATE 1.12.1 version (as it was in Ubuntu 16.04 LTS) user was able to scroll tabs of Pluma's Side Pane with mouse wheel.

#### Actual behaviour
In modern MATE versions as in Ubuntu 19.10 (development version) user is unable to scroll tabs of Pluma's Side Pane with mouse wheel.

#### Steps to reproduce the behaviour
1. Open Pluma
2. Go to View → Side Pane
3. Try to scroll shown tabs with mouse wheel

#### MATE general version
1.22.1

#### Package version
1.22.1-1

#### Linux Distribution
Ubuntu 19.10 (development version)

ProblemType: Bug
DistroRelease: Ubuntu 19.10
Package: pluma 1.22.1-1
ProcVersionSignature: Ubuntu 5.2.0-10.11-generic 5.2.4
Uname: Linux 5.2.0-10-generic x86_64
ApportVersion: 2.20.11-0ubuntu7
Architecture: amd64
CurrentDesktop: MATE
Date: Wed Aug 28 22:39:10 2019
InstallationDate: Installed on 2019-08-22 (6 days ago)
InstallationMedia: Ubuntu-MATE 19.10 "Eoan Ermine" - Alpha amd64 (20190822)
SourcePackage: pluma
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Norbert (nrbrtx)]

21.10 is still affected.

[Norbert (nrbrtx)]

Bug still exists in latest Ubuntu MATE 22.04 LTS.