MT#61101 ec2-create-ce: disable backports repository

On recent EC2 bookworm AMIs (as observed with our mr13.2.1 EC2 build
with AMI ID ami-09ca7561204a0d1d4), the bookworm-backports repository is
enabled by default:

|  admin@ip-10-0-0-204:~$ cat /etc/apt/sources.list.d/debian.sources
|  Types: deb deb-src
|  URIs: mirror+file:///etc/apt/mirrors/debian.list
|  Suites: bookworm bookworm-updates bookworm-backports
|  Components: main
|  Signed-By: /usr/share/keyrings/debian-archive-keyring.gpg
|
|  Types: deb deb-src
|  URIs: mirror+file:///etc/apt/mirrors/debian-security.list
|  Suites: bookworm-security
|  Components: main
|  Signed-By: /usr/share/keyrings/debian-archive-keyring.gpg

Our own valkey-server + valkey-tools backport has the identical *version*
number with a *higher* apt pinning though:

|  admin@ip-10-0-0-204:~$ apt-cache policy valkey-server valkey-tools
|  valkey-server:
|    Installed: 8.0.1+dfsg1-1~bpo12+1
|    Candidate: 8.0.1+dfsg1-1~bpo12+1
|    Version table:
|   *** 8.0.1+dfsg1-1~bpo12+1 100
|	  100 mirror+file:/etc/apt/mirrors/debian.list bookworm-backports/main amd64 Packages
|	  100 /var/lib/dpkg/status
|       8.0.1+dfsg1-1~bpo12+1 990
|	  990 https://deb.sipwise.com/spce/mr13.2.1 bookworm/main amd64 Packages
|  valkey-tools:
|    Installed: 8.0.1+dfsg1-1~bpo12+1
|    Candidate: 8.0.1+dfsg1-1~bpo12+1
|    Version table:
|   *** 8.0.1+dfsg1-1~bpo12+1 100
|	  100 mirror+file:/etc/apt/mirrors/debian.list bookworm-backports/main amd64 Packages
|	  100 /var/lib/dpkg/status
|       8.0.1+dfsg1-1~bpo12+1 990
|	  990 https://deb.sipwise.com/spce/mr13.2.1 bookworm/main amd64 Packages

This causes installer to fail therefor with:

| Making sure all packages are up to date ...
| Reading package lists...
| Building dependency tree...
| Reading state information...
| Calculating upgrade...
| The following packages will be DOWNGRADED:
|   valkey-server valkey-tools
| 0 upgraded, 0 newly installed, 2 downgraded, 0 to remove and 0 not upgraded.
| E: Packages were downgraded and -y was used without --allow-downgrades.
| ABORTED: Error upgrading packages

We need to make sure that such a backports repository isn't enabled by
default.

Change-Id: I3fbba0b897479109ba44df43bafd7fff89647a25

ec2-create-ce

@@ -453,6 +453,12 @@ if [ -f /etc/apt/sources.list.d/backports.list ] && grep -q 'jessie-backports' /
   rm -f /etc/apt/sources.list.d/backports.list
 fi
 
+# workaround for mr13.2.1 and newer with bookworm-backports enabled by default:
+if [ -f /etc/apt/sources.list.d/debian.sources ] && grep -q '-backports' /etc/apt/sources.list.d/debian.sources ; then
+  echo "backports is unexpected, disabling from /etc/apt/sources.list.d/debian.sources"
+  sed -i -E 's/ [a-z]+-backports//' /etc/apt/sources.list.d/debian.sources
+fi
+
 if [ "${SYSTEMD_SUPPORT}" = "false" ] && [ -d /run/systemd/system ] ; then
   echo "Switching from systemd to sysvinit (pre-reboot)"
   apt update