[0.14.0] Backport "Add warning when all sources are selected for deletion" #2318

Job	Run time
build-debs (bookworm)	2m 50s
lintian (bookworm)	4m 2s
verify-builder-sync (bookworm)	46s
piuparts (client, bookworm)	2m 58s
piuparts (export, bookworm)	2m 23s
piuparts (keyring, bookworm)	1m 39s
piuparts (log, bookworm)	1m 33s
piuparts (proxy, bookworm)	1m 30s
piuparts (qubesdb-tools, bookworm)	1m 22s
piuparts (whonix-config, bookworm)	1m 41s
reproducible-debs (bookworm)	15s
	20m 59s

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