Merge simpoir-buildd_unpin_backports into ubuntu/master [a=simpoir] [r=philroche,utkarsh]

Unpin backports priority for buildd images.

There was a time historically where Launchpad buildd might have relied
on that behaviour, but this shouldn't be the case anymore as it sets
priority manually when building backports.
Meanwhile any other builds using buildd images (e.g. snapcraft)
shouldn't default to backports unless required. (lp: #2009871)
Refs:
- [1] https://git.launchpad.net/launchpad-buildd/commit?id=c2ebcb6752

MP: https://code.launchpad.net/~simpoir/livecd-rootfs/+git/livecd-rootfs/+merge/460194

debian/changelog

@@ -1,3 +1,10 @@
+livecd-rootfs (24.04.41) noble; urgency=medium
+
+  * live-build/buildd/includes.chroot/etc/apt:
+    unpin backports for buildd images (lp: #2009871)
+
+ -- Simon Poirier <simon.poirier@canonical.com>  Thu, 22 Feb 2024 12:02:50 -0500
+
 livecd-rootfs (24.04.40) noble; urgency=medium
 
   [ Sean Davis ]

live-build/buildd/includes.chroot/etc/apt/preferences.d/backports

@@ -1,3 +0,0 @@
-Package: *
-Pin: release a=*-backports
-Pin-Priority: 500