git: openjdk/jdk: 8306630: Bump minimum boot jdk to JDK 21

[Mikael Vidstedt]

Changeset: 83c0e451
Author:    Mikael Vidstedt <mikael at openjdk.org>
Date:      2023-09-28 00:17:31 +0000
URL:       https://git.openjdk.org/jdk/commit/83c0e4516064846c956d9a760338e71be1593f6f

8306630: Bump minimum boot jdk to JDK 21

Reviewed-by: darcy, erikj, iris, shade

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