Pin pubsub emulator docker version

[amarziali]

What Does This Do

The new image just published seems not having java installed in the container hence the emulator does not start. Here we pin the emulator to the latest working one

Motivation

Additional Notes

Contributor Checklist

• Format the title according the contribution guidelines
• Assign the type: and (comp: or inst:) labels in addition to any usefull labels
• Squash your commits prior merging or merge using GitHub's Squash and merge
• Don't use close, fix or any linking keywords when referencing an issue.
  Use solves instead, and assign the PR milestone to the issue
• Update the public documentation in case of new configuration flag or behavior

Jira ticket: [PROJ-IDENT]