fix: make sure pixi vars are available before activation.env vars are…

[ruben-arts]

fixes: #1726

pixi shell-hook before:

export ABC="$PIXI_PROJECT_ROOT/test"
...
export PIXI_PROJECT_ROOT="/home/rarts/dev/pixi"

pixi shell-hook after:

...
export PIXI_PROJECT_ROOT="/home/rarts/dev/pixi"
...
export ABC="$PIXI_PROJECT_ROOT/test"

[nichmor]

I think it will be good to add a small test to validate ( and show ) what correct order we expect from pixi shell-hook

[nichmor]

LGTM after adding the test

[ruben-arts]

Because you @nichmor made me make a test I found another bug!