RFR: 8315863: [GHA] Update checkout action to use v4

Thu Sep 7 16:29:51 UTC 2023

On Thu, 7 Sep 2023 16:16:36 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> Please wait for GHA to complete before integrating GHA patches!

Yes, sure. Next time, I'll wait for completion - this time, I checked that `actions/checkout at v4` steps were successfully run in https://github.com/openjdk/jdk/pull/15620/checks

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PR Comment: https://git.openjdk.org/jdk/pull/15620#issuecomment-1710452932