Using the shell installer with macOS and fish, bin is not available after shell restart

A user has reported that after following the official installer via `curl | sh`, they are able to run the `edgedb` command _within that terminal session_ but surprisingly _not_ after a terminal restart. They are using fish as their shell. According to the output (screenshot attached), the installer is detecting that it should not update the PATH since it already seems to be in the PATH, but that is surely a false positive. Also note that it doesn't seem to be able to find the tmpdir it made.

Reproduce the official curl | sh installer on macOS using fish, then restart the terminal and check whether edgedb remains available. Inspect the installer output around PATH detection and temporary-directory handling; done means the installed command is available after restart and the installer handles the detected PATH and tmpdir correctly.

Written by the indexing model from the issue text.