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

[Thomas Schatzl]

On Mon, 25 Jul 2022 10:53:52 GMT, Kim Barrett <kbarrett 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.

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Marked as reviewed by tschatzl (Reviewer).

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