chore: run tests with Python 3.10 (#1407)

Co-authored-by: Anthonios Partheniou <partheniou@google.com>

noxfile.py

@@ -14,19 +14,19 @@
 
 import nox
 
-@nox.session(python=['3.6'])
+@nox.session(python=['3.6', '3.10'])
 def generate_protos(session):
     session.install("grpcio-tools")
     session.run(
         "python", "-m", "grpc_tools.protoc", "-Isynthtool/protos", "--python_out=synthtool/protos", "synthtool/protos/metadata.proto", "synthtool/protos/preconfig.proto")
 
-@nox.session(python=['3.6', '3.9'])
+@nox.session(python=['3.6', '3.10'])
 def blacken(session):
     session.install('black==22.3.0', 'click>8.0')
     session.run('black', 'synthtool', 'tests')
 
 
-@nox.session(python=['3.6', '3.8', '3.9'])
+@nox.session(python=['3.6', '3.10'])
 def lint(session):
     session.install('mypy==0.790', 'flake8', 'black==22.3.0')
     session.run('pip', 'install', '-e', '.')
@@ -36,7 +36,7 @@ def lint(session):
     session.run('mypy', 'synthtool')
 
 
-@nox.session(python=['3.6', '3.8'])
+@nox.session(python=['3.6', '3.10'])
 def test(session):
     session.install('pytest', 'pytest-cov', 'requests_mock', 'watchdog', 'flake8')
     session.run('pip', 'install', '-e', '.')