Summary:
the latest pex release (2.45.2) broke the workflow for creating a PEX_ROOT with its mkdtemp implementation.

The easy fix from our side is to ensure the directory exists and is writeable, rather then
having pex create it for us in the /tmp directory

Test Plan: built pex with the new dockerfile, it passes

Reviewers: muthu, jharveysmith, nsingh

Reviewed By: jharveysmith, nsingh

Subscribers: nsingh

Differential Revision: https://phorge.dev.yugabyte.com/D45375