(maint) Add ability to specify a ref to compare against

[AdmiringWorm]

Description Of Changes

This change allows the GitHub action workflow to specify a specific
reference to be used when finding files to send to the language server.

This allows the the languagetool check to use less time by only compare
any new or changed files, instead of running all of the files in the
repository through the language server.

Additional work is needed for repositories after this change is merged.

Motivation and Context

To speed up the processing in large repositories, and not check any files that isn't needed to be checked.

Testing

1. Tested in one of my own forks.
2. Not found a way to test it locally.

Operating Systems Testing

N/A

Change Types Made

• Bug fix (non-breaking change).
• Feature / Enhancement (non-breaking change).
• Breaking change (fix or feature that could cause existing functionality to change).
• Documentation changes.
• PowerShell code changes.

Change Checklist

• Requires a change to the documentation.
• Documentation has been updated.
• Tests to cover my changes, have been added.
• All new and existing tests passed?
• PowerShell code changes: PowerShell v2 compatibility checked?

Related Issue

N/A

[pauby]

LGTM!