Describe the bug

This works correctly

pipx install "mycli[extras]"

but this doesn't

pipx install "mycli[extras]"
pipx upgrade "mycli[extras]"

and it fails with

Package is not installed. Expected to find /path/to/pipx/venvs/mycli[isolated], but it does not exist.

How to reproduce
For reproduction, I suggest

pipx install "coverage[toml]"
pipx upgrade "coverage[toml]"

Expected behavior
I'm not 100% sure what should happen actually, but the current error message seems broken (of course a directory with [ and ] in its name wasn't found).
I think the upgrade should go through wether or not the extra targets match the ones I used (or didn't use) the first time I installed the CLI (here coverage).

I'd be happy to contribute a patch, but I'd appreciate some guidance regarding what the expected behaviour should be.