Fix compatibility with setuptools 72

Due to test command removal in setuptools, installation fails with version 72:

# pip wheel --no-cache-dir --use-pep517 "gojsonnet (==0.20.0)"
Collecting gojsonnet==0.20.0
  Downloading gojsonnet-0.20.0.tar.gz (7.4 MB)
     ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 7.4/7.4 MB 15.0 MB/s eta 0:00:00
  Installing build dependencies ... done
  Getting requirements to build wheel ... error
  error: subprocess-exited-with-error

  × Getting requirements to build wheel did not run successfully.
  │ exit code: 1
  ╰─> [17 lines of output]
      Traceback (most recent call last):
        File "/usr/local/lib/python3.10/site-packages/pip/_vendor/pyproject_hooks/_in_process/_in_process.py", line 353, in <module>
          main()
        File "/usr/local/lib/python3.10/site-packages/pip/_vendor/pyproject_hooks/_in_process/_in_process.py", line 335, in main
          json_out['return_val'] = hook(**hook_input['kwargs'])
        File "/usr/local/lib/python3.10/site-packages/pip/_vendor/pyproject_hooks/_in_process/_in_process.py", line 118, in get_requires_for_build_wheel
          return hook(config_settings)
        File "/tmp/pip-build-env-i9xslfbh/overlay/lib/python3.10/site-packages/setuptools/build_meta.py", line 327, in get_requires_for_build_wheel
          return self._get_build_requires(config_settings, requirements=[])
        File "/tmp/pip-build-env-i9xslfbh/overlay/lib/python3.10/site-packages/setuptools/build_meta.py", line 297, in _get_build_requires
          self.run_setup()
        File "/tmp/pip-build-env-i9xslfbh/overlay/lib/python3.10/site-packages/setuptools/build_meta.py", line 497, in run_setup
          super().run_setup(setup_script=setup_script)
        File "/tmp/pip-build-env-i9xslfbh/overlay/lib/python3.10/site-packages/setuptools/build_meta.py", line 313, in run_setup
          exec(code, locals())
        File "<string>", line 19, in <module>
      ModuleNotFoundError: No module named 'setuptools.command.test'

pytest advises to not integrate with setuptools anymore, thus I've dropped that part.

google / go-jsonnet

Fix compatibility with setuptools 72 #763