Fix version bump workflow on call

[vgrassia]

Type of change

- [ ] Bug fix
- [ ] New feature development
- [ ] Tech debt (refactoring, code cleanup, dependency upgrades, etc)
- [X] Build/deploy pipeline (DevOps)
- [ ] Other

Objective

This PR updates the checkout step to always be master. This limits the use of the workflow to only bump the version on master, but we shouldn't be using it on any other branch anyways. This was needed because when the workflow was called from another repository it was checking out the wrong repository.

Code changes

• .github/workflows/version-bump.yml: Force checkout step to use master and create PR for merging into master.

Before you submit

• Please check for formatting errors (dotnet format --verify-no-changes) (required)
• If making database changes - make sure you also update Entity Framework queries and/or migrations
• Please add unit tests where it makes sense to do so (encouraged but not required)
• If this change requires a documentation update - notify the documentation team
• If this change has particular deployment requirements - notify the DevOps team