CI: Update and pin actions/checkout to v7.0.1

[RytoEX]

Description

CI: Update and pin actions/checkout to v7.0.1

Motivation and Context

Keep up to date. Remove CI warnings.

How Has This Been Tested?

CI will validate.

Types of changes

• CI
• Tweak (non-breaking change to improve existing functionality)

Checklist:

• I have read the contributing document.
• My code has been run through clang-format.
• My code follows the project's style guidelines
• My code is not on the master branch.
• My code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.