RFR: 8275512: Upgrade required version of jtreg to 6.1

[Magnus Ihse Bursie]

On Tue, 19 Oct 2021 13:51:45 GMT, Weijun Wang <weijun at openjdk.org> wrote:

> As a follow up of JEP 411, we will soon disallow security manager by default. jtreg 6.1 does not set its own security manager if JDK version is >= 18.

LGTM

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Marked as reviewed by ihse (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/6012