chromium security update blocked by new dependency from stable

[eMPee584]

Contrary to #146 there are (probably quite rare) situations, where one might want to accept a new dependency (sse3-support) requested by a to-be-updated package (chromium), without adding the full archive (stable) to the whitelist.. Maybe you have an idea how to handle side cases like that.. 🥲
Here's the dry-run log of the situation:
unattended-upgrades-dry-run.chromium-security-update-blocked-by-sse3-support-dependency.log

[julian-klode]

stable really ought to be part of the allowed set if stable-foo is

[eMPee584]

But we want security updates only, not all possible updates.