Straightforward update of some tests which use core reflection to set the `Thread.Builder` scheduler.
------------- Commit messages: - 8369997: Tests that use custom scheduler should use jdk.test.lib.thread.VThreadScheduler Changes: https://git.openjdk.org/jdk/pull/27855/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27855&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8369997 Stats: 69 lines in 3 files changed: 9 ins; 53 del; 7 mod Patch: https://git.openjdk.org/jdk/pull/27855.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/27855/head:pull/27855 PR: https://git.openjdk.org/jdk/pull/27855
