chore(spanner): Issue#1143 - Update dependency

[bhatt4982]

chore(spanner): Issue#1143 - Update dependency

• Move grpc-interceptor to extras_required named testing

Fixes #1143 🦕

[harshachinta]

@bhatt4982 The presubmits are failing since the tetsing dependency is not getting installed when installing depenedencies.
You will need to add this testing dependency as extra similar to tracing ones here. ex: pip install mypackage[tracing, testing]

1. python-spanner/noxfile.py

   Line 60 in 1659ed3

   SYSTEM_TEST_EXTRAS: List[str] = [

2. Please look at references to tracing and add testing at appropriate places
   

   python-spanner/noxfile.py

   Line 168 in 1659ed3

   session.install("-e", ".[tracing]", "-c", constraints_path)

This reference might help you understand
https://packaging.python.org/en/latest/tutorials/installing-packages/#installing-extras

[harshachinta]

@bhatt4982

1. We will need to update owlbot.py https://github.com/googleapis/python-spanner/blob/112e74e6f15dc883dc347e82c890251c53a51a02/owlbot.py#L131C26-L131C33 to add testing dependency similar to tracing. Otherwise the automated PR might remove these changes,
2. Can you fix the lint? Command: nox -s blacken

[harshachinta]

@parthea Can you help with a quick review of this PR?