RFR: 8274083: Update testing docs to mention tiered testing [v3]

[Aleksey Shipilev]

On Thu, 23 Sep 2021 10:56:02 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

>> Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   More fixes
>
> doc/testing.md line 95:
> 
>> 93: the tests in `tier1` are carefully selected and optimized to run fast, and to run in the
>> 94: most stable manner. The test failures in `tier1` are usually followed up on quickly, either
>> 95: with fixes, or adding relevant tests to problem list. [GitHub Actions workflows](../.github/workflows/),
> 
> I don't think the link to the `.github` directory makes sense here. If there should be a link at all, it should point to information on how GHA works and how to enable these. And frankly I'm not sure if any such comprehensive documentation exists. :-( Perhaps in the Skara wiki? Otherwise the link is just distracting.

Sure, I actually put the link there very optimistically :) Dropped it in the new commit.

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PR: https://git.openjdk.java.net/jdk/pull/5615