[DOCS] Processing changed files does not include full git history

[BernieWhite]

URL

https://microsoft.github.io/PSRule/v3/creating-your-pipeline/

How could the documentation be improved?

To compare changed files full git history must be fetched. Both GitHub Actions and Azure Pipelines to a shallow fetch be default.

The instructions and examples need to be updated to include this as a required step for processing changes files only to work.

GitHub Actions:

- uses: actions/checkout@v4
  with:
    fetch-depth: 0

Azure Pipelines

  # Checkout the repository
  - checkout: self
    fetchDepth: 0

Additional context

Discussed here: #1465 (comment)