mate-themes package for Ubuntu MATE: Use Ubuntu icon for the "Ubuntu base" package in `update-manager`

[davidhedlund]

Expected behaviour

The "Ubuntu base" package is used by Ubuntu flavors (Ubuntu, Ubuntu MATE, etc). So all themes in mate-themes should use the Ubuntu logo for the "Ubuntu base" package entry in the update-manger. All themes in the yaru-theme-gtk do this, see for example the Yaru-MATE-light that is used as the default theme in Ubuntu MATE 23.04:

• Observe that YaruGreen, and YaruOK, in the mate-themes package do not use Ubuntu icon.
• /etc/os-release in all Ubuntu flavours lists LOGO=ubuntu-logo` which can be used to determine the logo name.

Actual behaviour

Steps to reproduce the behaviour

MATE icon:

• BlackMATE
• Blue-Submarine
• BlueMenta
• ContrastHighInverse
• Green-Submarine
• GreenLaguna
• High Contrast Inverse
• Menta
• TraditionalGreen
• TraditionalOk
• YaruGreen
• YaruOK

Debian icon:

• High Contrast

MATE general version

1.26.0

Package version

1.26.0

Linux Distribution

Ubuntu MATE 23.04

Link to bugreport of your Distribution (requirement)

[davidhedlund]

Self-reminder: Reopen and rewrite this Trisquel issue when this issue has been solved: https://gitlab.trisquel.org/trisquel/package-helpers/-/issues/109