gsutil installation fails via pip from local repo

I am trying to create a local pip repo for gsutil (for air gap environment). For that I am downloading all the dependencies and gsutil using followinn commands.

# python3 -m pip download --no-binary=:all: gsutil

or

# pip-download gsutil

This downloads all the dependencies and gsutil and I am trying to install on a different platform hence I use only source from here.
But the problem is with the mock package.
In gsutil mock dependency is defined as "mock==2.0.0" so only version 2.0.0 is downloaded and get installed.
But version 2.0.0 has issue
testing-cabal/mock#467
I need the latest version but if I put latest version in the repo that doesn't work if I use pip command to install gsutil.
I think gsutil should relax the dependency to "mock>=2.0.0"
I am not finding a solution for this.