packages.yaml was merged in main before 0.12.7 and 0.12.8 releases but it did not run both of the times.

It seems like the trigger,

on:
  release:
    types: [published]

is not working.

There is some context and a similar issue. googleapis/release-please#766

A workaround can be to change the trigger to,

on:
  workflow_run:
    workflows: [release]
    types:
      - completed

This will run the workflow after the release workflow.

Another approach is to create a separate token, as discussed here, https://github.com/orgs/community/discussions/26875

cc @deansheather