RFR: JDK-8268185: Update GitHub Actions for jtreg 6

[Erik Joelsson]

On Thu, 3 Jun 2021 19:05:35 GMT, Jonathan Gibbons <jjg at openjdk.org> wrote:

> Please review changes to the GitHub Actions for the repo, to use jtreg 6.
> 
> There are three small parts to the change:
> 
> 1. The version info is updated in `make/conf/test-dependencies`
> 2. The new `make/build.sh` script is used to build `jtreg`, instead of the earlier `build-all.sh` script
> 3. The format of the tag in the jtreg repo is changed to follow OpenJDK conventions.
> 
> Tested implicitly with GitHub Actions on my fork, seen here:
> https://github.com/jonathan-gibbons/jdk/actions/runs/903574304

Marked as reviewed by erikj (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/4343