Set the correct license on docker images

[hughns]

Previously the docker/metadata action was autodetecting the license and only getting AGPL not dual license.

[hughns]

Currently I have no way to test this PR in our CI.

This is because the pr-deploy.yaml workflow (which in turn calls the build-and-publish-docker.yaml workflow) is triggered by the completion of the build.yaml workflow. This means that pr-deploy.yaml is always run from the default (i.e. livekit) branch and in turn the build-and-publish-docker.yaml is run from livekit.

This is sub-optimal.

To fix could:

• combine the pr-deploy.yaml steps into the build.yaml directly
• call pr-deploy.yaml from build.yaml explicitly

In the meantime I'm going to just merge this PR and test on livekit branch.

[fkwp]

lgtm

[hughns]

This is working in so far as the expected licenses label is appearing in https://github.com/element-hq/element-call/actions/runs/14408255425/job/40410011160