JobScheduler unit tests

[HansenSven]

Description

The JobScheduler layer didnt have any tests till this PR.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist

• My code follows the style guidelines of this project
• I did not update API Controllers, if I did, I added/changed Postman or XUnit integration tests
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I updated the changelog with an end-user readable description
• I assigned this pull request to the correct project board to update the sprint board

Steps to Test or Reproduce

1. Open the dex-backend project
2. Run the tests within the JobScheduler.Tests project
3. Make sure they respond successfull

Issue

Closes: #381