git: openjdk/jdk: 8300868: Reduce visibility in java.io.SerialCallbackContext

[Per Minborg]

Changeset: a7f035db
Author:    Per Minborg <pminborg at openjdk.org>
Date:      2023-01-23 17:47:01 +0000
URL:       https://git.openjdk.org/jdk/commit/a7f035db762ce44b72733094422488047c9ad738

8300868: Reduce visibility in java.io.SerialCallbackContext

Reviewed-by: rriggs

! src/java.base/share/classes/java/io/SerialCallbackContext.java