Update actions/checkout action to v4

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
actions/checkout	action	major	v3 -> v4

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Release Notes

actions/checkout (actions/checkout)

v4

Compare Source

• url-helper.ts now leverages well-known environment variables by @​jww3 in https://github.com/actions/checkout/pull/1941
• Expand unit test coverage for isGhes by @​jww3 in https://github.com/actions/checkout/pull/1946

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[sourcery-ai]

Reviewer's Guide

This PR implements a straightforward upgrade of the GitHub Actions checkout step by bumping the actions/checkout version from v3 to v4 in the validate workflow.

File-Level Changes

Change	Details	Files
Upgrade actions/checkout action to v4	Changed the version specifier in the checkout step from v3 to v4	.github/workflows/validate.yaml

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