workflow action version

[jeffjennings]

Updates the version of 'peter-evans/repository-dispatch' in the build.yml workflow.

The workflow is currently failing due to 'Bad credentials' - the secrets.DISPATCH_GITHUB_TOKEN likely needs to be updated. I don't have permissions to edit the repo secrets.

• Check the box to confirm that you are familiar with the contributing guidelines and/or indicate (check the box) that you are familiar with our contributing workflow.
• Confirm that any contributed tutorials contain a complete Introduction which includes an Author list, Learning Goals, Keywords, Companion Content (if applicable), and a Summary.
• Check the box to confirm that you are familiar with the Astropy community code of conduct and you agree to follow the CoC.

[jeffjennings]

Closing - this is superseded by #609

[pllim]

ooops sorry... I didn't realize.