add release prep secret

[emmyoop]

Description

The release currently fails because IT_TEAM_MEMBERSHIP secret is not being passed in to the release-prep workflow. This was an oversight in a previous update to add core team automation because while the release-prep workflow defines the secret, dbt-spark doesn't actually use the secret right now. This is because dbt-spark is still on CircleCI and so the release-prep workflow just makes sure the version is already bumped and changelog exists. It does not trigger the version bump and changelog generation itself.

Checklist

• [ ] I have read the contributing guide and understand what's expected of me
• [ ] I have signed the CLA
• [ ] I have run this code in development and it appears to resolve the stated issue
• [ ] This PR includes tests, or tests are not required/relevant for this PR
• [ ] I have opened an issue to add/update docs, or docs changes are not required/relevant for this PR
• [ ] I have run changie new to create a changelog entry

[github-actions[bot]]

Thank you for your pull request! We could not find a changelog entry for this change. For details on how to document a change, see the dbt-spark contributing guide.