Fix typo on gpu testing docs.

'o' should have been '#' in one section.

Bug: None
Change-Id: I458e1f7300e8ea9a2607d23ee1d80e039acc9879
Tbr: [email protected]
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1879308
Reviewed-by: Jamie Madill <[email protected]>
Commit-Queue: Jamie Madill <[email protected]>
Cr-Commit-Position: refs/heads/master@{#709078}
1 file changed