Check references to master

The master branch of this repository has been migrated to main using the [master-to-main](https://github.com/guardian/master-to-main) tool.

Some files in the repository contain the word master. Please check the following files and update where required:

- [ ] [test/lib/GitChangesSpec.scala](https://github.com/guardian/prout/blob/main/test/lib/GitChangesSpec.scala)
- [ ] [test/FunctionalSpec.scala](https://github.com/guardian/prout/blob/main/test/FunctionalSpec.scala)
- [ ] [test/lib/ConfigFinderSpec.scala](https://github.com/guardian/prout/blob/main/test/lib/ConfigFinderSpec.scala)
- [ ] [app/lib/RepoSnapshot.scala](https://github.com/guardian/prout/blob/main/app/lib/RepoSnapshot.scala)
- [ ] [notes.md](https://github.com/guardian/prout/blob/main/notes.md)
- [ ] [test/lib/Helpers.scala](https://github.com/guardian/prout/blob/main/test/lib/Helpers.scala)
- [ ] [artwork/prout-pull-request-history-diagram.svg](https://github.com/guardian/prout/blob/main/artwork/prout-pull-request-history-diagram.svg)

Review the listed files, starting with test/lib/GitChangesSpec.scala and app/lib/RepoSnapshot.scala, and search each for references to “master.” Check whether each occurrence is still intentional after the branch migration, update the required references, and verify the affected tests and documentation remain consistent.

Written by the indexing model from the issue text.