Validate Dependabot configs in CI

[JonZeolla]

We should do this both in the parent and the generated project's GitHub Actions, however it's blocked on dependabot/dependabot-core#4605

We recently encountered a failure due to this:

Your .github/dependabot.yml contained invalid details
Dependabot encountered the following error when parsing your .github/dependabot.yml:

The property '#/updates/2/directory' must not include a glob pattern
Please update the config file to conform with Dependabot's specification.

[JonZeolla]

Possible workaround: https://github.com/marocchino/validate-dependabot