Remove extra usage of 'repository' in understanding-github-actions.md

[tmelliottjr]

Code of Conduct

• I have read and agree to the GitHub Docs project's Code of Conduct

What article on docs.github.com is affected?

https://docs.github.com/en/actions/learn-github-actions/understanding-github-actions

What part(s) of the article would you like to see updated?

The section on workflows uses the word 'repository' twice and makes the sentence less readable.

Additional information

No response

[welcome]

Thanks for opening this issue. A GitHub docs team member should be by to give feedback soon. In the meantime, please check out the contributing guidelines.