Standardize `update-types` Format in Dependabot Configuration

[yeikel]

Is there an existing issue for this?

• I have searched the existing issues

Feature description

The current implementation of update-types in Dependabot is inconsistent: some contexts require the version-update:<type> format (e.g., in the ignore block), while others accept just <type> (e.g., in groups).

Examples from this project:

Groups:

https://github.com/dependabot/dependabot-core/blob/2e2a61a27ffd35f444d9096a3fe0c73bca3fc972/.github/dependabot.yml#L30C9-L33

Ignore:

dependabot-core/.github/dependabot.yml

Line 123 in 2e2a61a

update-types: [ "version-update:semver-major" ]

This inconsistency is confusing for users and increases the likelihood of configuration errors. It would be great if we could standardize this under <type> to reduce the configuration complexity.

In fact, this is so confusing that even the docs are wrong: github/docs#40031