fix: make multi-ecosystem patterns optional

[Solaris-star]

Fixes #6219

Removes the conditional that required patterns whenever multi-ecosystem-group is present. GitHub documents patterns as optional in this configuration, with omission applying the group to all dependencies in the ecosystem.

Validation:

• python3 -m json.tool src/schemas/json/dependabot-2.0.json
• npm run prettier
• npm run typecheck
• npm run eslint

[github-actions]

Thanks for the PR!

This section of the codebase is owned by @madskristensen and @hyperupcall - if they write a comment saying "LGTM" then it will be merged.

[madskristensen]

Thanks!