RFR: 8290959: Consistently use "grey" instead of "gray" in GC code

[Kim Barrett]

On Mon, 25 Jul 2022 11:08:49 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

>> Please review this trivial spelling change in some comments to make them
>> consistent with the spelling in identifier names.
>
> Looks good and trivial.

Thanks for reviewing @tschatzl .

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PR: https://git.openjdk.org/jdk/pull/9625