[Chore] Use newer nix in all CI steps

Description

Problem: The CI runners are now capable of using a newer nix version by setting the USE_NEWER_NIX env variable. We want to use this new possibility because nix 2.4 seemed to work for us in the past and eventually we expect for the runners to switch to it again.

Solution: Set the env variable and change the nix command in all CI pipeline's steps.

Note: this is a "Draft" because waiting for said new capability.

Related issue(s)

None

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