chore(gapic-generator): update noxfile in redis_selective golden

Author: chalmerlowe

packages/gapic-generator/tests/integration/goldens/redis_selective/noxfile.py

@@ -485,7 +485,8 @@ def prerelease_deps(session, protobuf_implementation):
     ]
 
     # Install dependencies specified in `testing/constraints-X.txt`.
-    session.install(*constraints_deps)
+    if constraints_deps:
+        session.install(*constraints_deps)
 
     # Note: If a dependency is added to the `prerel_deps` list,
     # the `core_dependencies_from_source` list in the `core_deps_from_source`
@@ -578,7 +579,8 @@ def core_deps_from_source(session, protobuf_implementation):
     ]
 
     # Install dependencies specified in `testing/constraints-X.txt`.
-    session.install(*constraints_deps)
+    if constraints_deps:
+        session.install(*constraints_deps)
 
     # TODO(https://github.com/googleapis/gapic-generator-python/issues/2358): `grpcio` and
     # `grpcio-status` should be added to the list below so that they are installed from source,