Turns out I misread the first result on Google. I incorrectly assumed that they were referring to the terminal shell (and when they said shell later on I assumed they meant $SHELL, although I should’ve been tipped off by the fact that shell wasn’t capitalized). Instead they were referring to the vim shell setting, which incorrectly had the -i flag instead of the -l flag.
So in case anyone else has this issue, go into your .vimrc and change make sure the line that sets your shell looks like this:
set shell=/bin/zsh\ -l
(Replacing /bin/zsh with the value of which zsh if it’s installed in a non-standard location, of course).
Reference commit: https://github.com/devx/vimified/commit/772e130c9c359ac87927a963e00a9cc6597cd170
