Add annotation toggle hotkey

[aaron-tdouble]

What article on docs.github.com is affected?

https://docs.github.com/en/github/getting-started-with-github/keyboard-shortcuts#source-code-browsing

What part(s) of the article would you like to see updated?

Github now allows a shortcut of a on to show and hide all annotations on a file diff.

[welcome]

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