Search options/filters broken after Bootstrap 5 upgrade

[osma]

At which URL did you encounter the problem?

https://dev.finto.fi/yso/en/search?clang=en&q=cat

What steps will reproduce the problem?

1. Perform a search (e.g. "cat" in YSO) and press Enter to get to the search result page
2. Look at the search options sidebar on the left

What is the expected output? What do you see instead?

Expected to see filters that can be used to narrow the search, like this (finto.fi / skosmos 2.14):

(Here, I've clicked on "By group" to open the list of possible groups)

But instead, the filters are not displaying normally and the lists of values cannot be opened:

I think this is a side effect of the Bootstrap 5 upgrade (#1182), ping @kinow

What browser did you use? (eg. Firefox, Chrome, Safari, Internet explorer)

Firefox