Fix AppVeyor to run only for changes to source

[johlju]

Pull Request (PR) description

This Pull Request (PR) fixes the following issues

None

Task list

• [x] Added an entry to the change log under the Unreleased section of the file CHANGELOG.md. Entry should say what was changed and how that affects users (if applicable), and reference the issue being resolved (if applicable).
• [ ] Resource documentation updated in the resource's README.md.
• [ ] Resource parameter descriptions updated in schema.mof.
• [ ] Comment-based help updated, including parameter descriptions.
• [ ] Localization strings updated.
• [ ] Examples updated.
• [ ] Unit tests updated. See DSC Community Testing Guidelines.
• [ ] Integration tests updated (where possible). See DSC Community Testing Guidelines.
• [ ] Code changes adheres to DSC Community Style Guidelines.

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This change is 

[codecov[bot]]

Codecov Report

Merging #1776 (ac11315) into main (c560fa0) will not change coverage. The diff coverage is n/a.

@@         Coverage Diff          @@
##           main   #1776   +/-   ##
====================================
  Coverage    86%     86%           
====================================
  Files        37      37           
  Lines      6261    6261           
====================================
  Hits       5422    5422           
  Misses      839     839           

Flag	Coverage Δ
unit	86% <ø> (ø)