RFR: 7903553: Update GitHub checkout action to v4

Thu Sep 7 15:45:06 UTC 2023

On Thu, 7 Sep 2023 14:13:58 GMT, Christian Stein <cstein at openjdk.org> wrote:

> Please review this change to update to use `actions/checkout at v4` in jtreg's GHA workflows.
> 
> Find the associated release notes here: https://github.com/actions/checkout/releases/tag/v4.0.0

Marked as reviewed by jjg (Lead).

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PR Review: https://git.openjdk.org/jtreg/pull/171#pullrequestreview-1615743703