Pull request changed files regression: cannot expand/collapse folders

[lornajane]

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The files explorer sidebar in pull requests seems to have "lost" some functionality in the last week or two - I'm attaching the screenshot of what Vimium can focus, which no longer includes the folders. Previously the folders could be expanded/collapsed (very helpful for navigating the changed files list, especially for users who can't scroll easily) but this is no longer the case. I'm a keyboard-only user and didn't find any other accessibility tools that did anything different. Could you please take a look?

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