What steps did you take and what happened?

Add check to validate PREVIOUS_RELEASE_TAG that it should contains rc or beta in the provided value.

For example

1. Generating notes for rc tag
   RELEASE_TAG=v1.7.x-rc.1 PREVIOUS_RELEASE_TAG=tags/v1.7.x-rc.0 make release-notes
2. Generating notes for beta tag
   RELEASE_TAG=v1.7.x-beta.1 PREVIOUS_RELEASE_TAG=tags/v1.7.x-beta.0 make release-notes

What did you expect to happen?

Validate should ensure that PREVIOUS_RELEASE_TAG is in correct format.

Cluster API version

v1.10

Kubernetes version

No response

Anything else you would like to add?

No response

Label(s) to be applied

/kind bug
One or more /area label. See https://github.com/kubernetes-sigs/cluster-api/labels?q=area for the list of labels.