Disable gRPC fork support in PortableRunnerTestWithSubprocesses (apache#38744)

Avoids deadline exceeded failures in subprocess tests. Redundant setup and
teardown in the multi-worker subclass are removed to inherit them cleanly.

Author: shunping

sdks/python/apache_beam/runners/portability/portable_runner_test.py

@@ -295,6 +295,22 @@ def create_options(self):
 class PortableRunnerTestWithSubprocesses(PortableRunnerTest):
   _use_subprocesses = True
 
+  # TODO(https://github.com/grpc/grpc/issues/37710): Remove once fixed.
+  @classmethod
+  def setUpClass(cls):
+    cls._old_fork_support = os.environ.get('GRPC_ENABLE_FORK_SUPPORT')
+    os.environ['GRPC_ENABLE_FORK_SUPPORT'] = 'false'
+    super().setUpClass()
+
+  # TODO(https://github.com/grpc/grpc/issues/37710): Remove once fixed.
+  @classmethod
+  def tearDownClass(cls):
+    if cls._old_fork_support is None:
+      os.environ.pop('GRPC_ENABLE_FORK_SUPPORT', None)
+    else:
+      os.environ['GRPC_ENABLE_FORK_SUPPORT'] = cls._old_fork_support
+    super().tearDownClass()
+
   def create_options(self):
     options = super().create_options()
     options.view_as(PortableOptions).environment_type = (
@@ -329,22 +345,6 @@ class PortableRunnerTestWithSubprocessesAndMultiWorkers(
     PortableRunnerTestWithSubprocesses):
   _use_subprocesses = True
 
-  # TODO(https://github.com/grpc/grpc/issues/37710): Remove once fixed.
-  @classmethod
-  def setUpClass(cls):
-    cls._old_fork_support = os.environ.get('GRPC_ENABLE_FORK_SUPPORT')
-    os.environ['GRPC_ENABLE_FORK_SUPPORT'] = 'false'
-    super().setUpClass()
-
-  # TODO(https://github.com/grpc/grpc/issues/37710): Remove once fixed.
-  @classmethod
-  def tearDownClass(cls):
-    if cls._old_fork_support is None:
-      os.environ.pop('GRPC_ENABLE_FORK_SUPPORT', None)
-    else:
-      os.environ['GRPC_ENABLE_FORK_SUPPORT'] = cls._old_fork_support
-    super().tearDownClass()
-
   def create_options(self):
     options = super() \
       .create_options()