Add a condition to handle -backports for bullseye #3

Job	Run time
build-container-image	1m 15s
Build dev-env (ubuntu-20.04)	2m 5s
Build dev-env (ubuntu-22.04)	1m 57s
Build dev-env (ubuntu-23.10)	2m 5s
Build dev-env (ubuntu-24.04)	1m 51s
Build dev-env (debian-bullseye)	1m 53s
Build dev-env (debian-bookworm)	1m 48s
Build dev-env (debian-trixie)	1m 53s
Build dev-env (fedora-39)	2m 6s
Build dev-env (fedora-40)	2m 7s
	19m 0s

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