Fix sidebar collapse when section has a collapsable sub-section

The following discussion from !2469 (merged) should be addressed:

• @jeldergl started a discussion: (+1 comment)

  @tauriedavis something seems to be broken with this extra nested level. It's always open and looks active by default, even when navigating to other pages. Closing it closes the parent too. I haven't been able to dig into this further, but it makes me wonder if something with the JS has to get updated.