[User feedback] Update Dependabot reference to include 15 character limit

[felicitymay]

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?

Configuration options for dependency updates

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

Currently the article does not mention that prefix and prefix-development have a 15 character limit. It would help users to know this information when they create their configuration for Dependabot.

Currently users only find out about the limit if they exceed it and get an error reported: The property '#/updates/0/commit-message/prefix' was not of a maximum string length of 15.

Additional information

No response