update build-debian-old to use Bullseye instead of EOL buster (valkey-io#2345)

Signed-off-by: Ran Shidlansik <[email protected]>

Author: ranshid

.github/workflows/ci.yml

@@ -70,7 +70,7 @@ jobs:
 
   build-debian-old:
     runs-on: ubuntu-latest
-    container: debian:buster
+    container: debian:bullseye
     steps:
       - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
       - name: make