Update APX branch in manifest_external_packages.yml

[tcompa]

Checklist before merging

• I added an appropriate entry to CHANGELOG.md

[tcompa]

This PR is meant to make the APX manifest-creation github action pass, but we still need @adrtsc to update the fractal-tasks-core dependency in APX (since it still depends on the pydantic-v2-second-attempt branch which doesn't exist any more).

Note that the other external-packages GitHub actions will keep failing until those packages update their manifest to a pydantic_v2 one.

[github-actions]

Coverage report

This PR does not seem to contain any modification to coverable code.

[tcompa]

This PR is meant to make the APX manifest-creation github action pass, but we still need @adrtsc to update the fractal-tasks-core dependency in APX (since it still depends on the pydantic-v2-second-attempt branch which doesn't exist any more).

Now working.