Python: Use spawn instead of fork for multiprocessing in tests

Set multiprocessing start method to "spawn" in conftest.py to avoid
fork() deprecation warnings when gRPC threads are present.

GrpcInterface/Python/rips/tests/conftest.py

@@ -1,6 +1,10 @@
 import pytest
 import sys
 import os
+import multiprocessing
+
+# Use spawn instead of fork to avoid deadlocks with gRPC threads
+multiprocessing.set_start_method("spawn", force=True)
 
 sys.path.insert(1, os.path.join(sys.path[0], "../../"))
 import rips