Describe the enhancement requested

When creating the Wheels for Python 3.12 we found a couple of issues around the installation of GCS testbench. One of the problems is we do use the same version of Python we are creating the wheels for than the one we use to install GCS testbench. This causes issues like no wheels available etcetera.

GCS testbench has added the ability to use pipx for the installation: googleapis/storage-testbench#545 (comment)

And as suggested here: #37901 (comment)
we should update our invocations on C++, Python and R tests.

We also should use a specific version of Python that works with the specific GCS testbench being used.

Component(s)

Continuous Integration, Python