[Bug] Accidental Breacking change with source-branches config

[david-driscoll]

Describe the bug
If the source branches configuration currently references master then upgrading to 5.6.5 will break gitversion.

Expected Behavior

Upgrading to 5.6.5 shouldn't see any breaking changes between versions

Actual Behavior

Upgrade to 5.6.5 causes a breaking change if the source-branches configuration references master

Possible Fix

Unsure

Steps to Reproduce

Example config:

assembly-versioning-scheme: MajorMinorPatch
mode: ContinuousDeployment
continuous-delivery-fallback-tag: ci
next-version: 0.1.0
branches:
  next:
    regex: ^next$
    mode: ContinuousDeployment
    tag: next
    increment: Major
    prevent-increment-of-merged-branch-version: false
    track-merge-target: false
    tracks-release-branches: false
    is-release-branch: false
    source-branches: ['master']
ignore:
  sha: []

If source-branches: ['master'] is changed to ``source-branches: ['main']` everything works again.

Context

#2570

Your Environment

Github Actions and local environment

• Version Used: 5.6.5
• Operating System and version (Windows 10, Ubuntu 18.04): All
• Link to your project: https://github.com/RocketSurgeonsGuild/Testing
• Link to your CI build (if appropriate): https://github.com/RocketSurgeonsGuild/Testing/actions/runs/546972012