[BUG] *.yml and *.targets files should contain copyright headers

[DaveTryon]

Please check whether the bug has already been filed.

Describe the bug

Our *.yml and *.targets files currently lack copyright headers. Suggested change:

1. Add *.yml and *.targets to the script to check for headers
2. Run the script to update the files
3. Include the updated files in the PR

To Reproduce Steps to reproduce the behavior:

Open any of the files under https://github.com/microsoft/axe-windows/tree/main/build

Expected behavior

These files should include copyright headers

Actual behavior

No copyright headers

Context

It probably makes sense to keep the script in sync with changes from https://github.com/microsoft/accessibility-insights-windows/issues/1761