Update pull request labeler schema

[Nick2bad4u]

Summary

• update the default pull-request-labeler schema to the current actions/labeler configuration shape
• preserve the old v4 schema as pull-request-labeler-4.json and move the old v4 fixtures under pull-request-labeler-4
• add support for changed-files-labels-limit and max-files-changed
• add a negative fixture for unsupported title rules

Validation

• node ./cli.js check --schema-name=pull-request-labeler.json
• node ./cli.js check --schema-name=pull-request-labeler-4.json
• node ./cli.js check --schema-name=pull-request-labeler-5.json
• checked C:/Repos/eslint-config-nick2bad4u/.github/labeler.yml against the updated default schema; it is invalid because official actions/labeler does not support body or title match rules

Source

• https://github.com/actions/labeler

[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.