fix order of --global flag for MacOS

[openrory]

• I have added a news fragment under changelog.d/ (if the patch affects the end users)

Summary of changes

This fixes issue #1429, the last step in the process of installing pipx for MacOS where it fails due to the --global flag being in the wrong order.

Test plan

1. uninstall pipx
2. install pipx in MacOS
3. use sudo pipx --global ensurepath instead of sudo pipx ensurepath --global

Tested by running

sudo pipx --global ensurepath

[chrysle]

Thanks, but this was already fixed in #1397, which makes the current flag order possible.