[ruby] disable ruby fork tests (#34443)

We see flakes on CI due to https://github.com/grpc/grpc/issues/34442, so
let's disable these tests until that's fixed.

tools/run_tests/run_tests.py

@@ -1015,15 +1015,12 @@ class RubyLanguage(object):
                 "src/ruby/end2end/prefork_without_using_grpc_test.rb",
                 "src/ruby/end2end/prefork_postfork_loop_test.rb",
             ]:
-                if platform_string() == "mac":
-                    # Skip fork tests on mac, it's only supported on linux.
-                    continue
-                if self.config.build_config == "dbg":
-                    # There's a known issue with dbg builds that breaks fork
-                    # support: https://github.com/grpc/grpc/issues/31885.
-                    # TODO(apolcyn): unskip these tests on dbg builds after we
-                    # migrate to event engine and hence fix that issue.
-                    continue
+                # Skip fork tests in general until https://github.com/grpc/grpc/issues/34442
+                # is fixed. Otherwise we see too many flakes.
+                # After that's fixed, we should continue to skip on mac
+                # indefinitely, and on "dbg" builds until the Event Engine
+                # migration completes.
+                continue
             tests.append(
                 self.config.job_spec(
                     ["ruby", test],