Use sparse checkout in Compliance job

[alzimmermsft]

Description

Updates the ci.yml Compliance job to use sparse checkout instead of checking out the entire repository. This reduces the amount of time used to checkout code in the job as the job only runs against code changed in the PR and pipelines are scoped to the specific files in an SDK group.

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.