Try to use udevadm settle after losetup to resolve race in riscv64 image builds.

debian/changelog

@@ -1,10 +1,15 @@
 livecd-rootfs (2.833) UNRELEASED; urgency=medium
 
+  [ Łukasz 'sil2100' Zemczak ]
   * Add ubuntucinnamon, ubuntu-unity and edubuntu to the workaround for the
     invalid apt cache issue we encountered during all of our previous
     releases.
   * Switch to use the desktop model for the installer for the canary images.
 
+  [ Steve Langasek ]
+  * Try to use udevadm settle after losetup to resolve race in riscv64 image
+    builds.
+
  -- Łukasz 'sil2100' Zemczak <lukasz.zemczak@ubuntu.com>  Wed, 26 Apr 2023 13:36:30 +0200
 
 livecd-rootfs (2.832) lunar; urgency=medium

live-build/functions

@@ -64,6 +64,8 @@ mount_image() {
     local rootpart="$2"
     loop_device=$(losetup --show -f -P -v ${backing_img})
 
+    udevadm settle
+
     if [ ! -b ${loop_device} ]; then
         echo "unable to find loop device for ${backing_img}"
         exit 1