Bug#1124683: mesa: version in backports conflicts with gnome

[NoisyCoil <noisycoil@debian.org>]

Source: mesa
Version: 25.2.6-1~bpo13+1
Severity: grave
Justification: renders package unusable
X-Debbugs-Cc: noisycoil@debian.org

Dear Maintainer,

At least some of the packages built from src:mesa in trixie-backports conflict
with gnome in trixie. To reproduce:

```
podman run -it --rm debian:trixie
apt-get install gnome
# Add the trixie-backports sources
apt-get install libegl-mesa0/trixie-backports
# Tries to uninstall gnome and a ton of dependencies
```

This is on arm64. I don't know if this bug also affects other architectures.

Cheers!