No path update happening if PIXI_NO_PATH_UPDATE is unset

[markusschlenker]

Checks

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pixi, using pixi --version.

Reproducible example

install.sh

Issue description

In the Linux installer install.sh the new option to suppress PATH update if the env variable PIXI_NO_PATH_UPDATE is set is working inverse of what is expected (at least as I understand it). If PIXI_NO_PATH_UPDATE is unset no PATH update happens. If PIXI_NO_PATH_UPDATE is assigned any value, the PATH update happens.

It appears the ! in the if clause was removed in #737. If I understand correctly, either the ! should be added again or -z be replaced by -n

[[ -n "${PIXI_NO_PATH_UPDATE-}" ]] && return

Expected behavior

If PIXI_NO_PATH_UPDATE is unset the PATH update happens (default). If PIXI_NO_PATH_UPDATE is assigned any value, the PATH update does not happens