RFR: 7903418: It is not possible to build jtreg 6.1 branch using jdk 11.0.18

[Christian Stein]

On Fri, 27 Jan 2023 03:01:40 GMT, Sergey Bylokhov <serb at openjdk.org> wrote:

> It is not possible to build the jtreg 6.X using the recently released JDK 11.0.18. The root cause is a grep command in the Defs.gmk which checks the usage of jdk8. Because of that, all GitHub actions for jdk17u-dev and jdk11u-dev are broken:
> see https://github.com/mrserb/jdk11u-dev/actions/runs/4018535809/jobs/6904278681

Jon created the tag `jtreg-6.1+3` ➡️ https://github.com/openjdk/jtreg/releases/tag/jtreg-6.1+3

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PR: https://git.openjdk.org/jtreg/pull/146