[ruby testing]: experimental change to grpc_class_init_test (#32337)

Let's see if this fixes the "Bus error" flakes that have been happening
in CI.

If it does, then we can narrow things down a bit. If flakes continue,
then we can revert this PR.

src/ruby/end2end/grpc_class_init_client.rb

@@ -36,13 +36,15 @@ end
 
 def run_gc_stress_test(test_proc)
   GC.disable
-  construct_many(test_proc)
+  # TODO(b/266212253): run construct_many
+  # in this test after "Bus error" flakes are fixed.
+  run_default_test(test_proc)
 
   GC.enable
-  construct_many(test_proc)
+  run_default_test(test_proc)
 
   GC.start
-  construct_many(test_proc)
+  run_default_test(test_proc)
 end
 
 def run_concurrency_stress_test(test_proc)
@@ -58,11 +60,10 @@ end
 
 # default (no gc_stress and no concurrency_stress)
 def run_default_test(test_proc)
-  thd = Thread.new do
-    test_proc.call
-  end
+  # TODO(b/266212253): re-enable the extra thread
+  # in this test after the "Bus error" flakes of this
+  # test are fixed.
   test_proc.call
-  thd.join
 end
 
 # rubocop:disable Metrics/CyclomaticComplexity

src/ruby/end2end/grpc_class_init_test.rb

@@ -30,7 +30,10 @@ def main
   # do a few runs for each config
   4.times do
     native_grpc_classes.each do |grpc_class|
-      ['', 'gc', 'concurrency'].each do |stress_test_type|
+      # TODO(b/266212253): re-enable the "concurrency" mode
+      # of this test after the "Bus error" flakes of this
+      # test are fixed.
+      ['', 'gc'].each do |stress_test_type|
         STDERR.puts 'start client'
         this_dir = File.expand_path(File.dirname(__FILE__))
         client_path = File.join(this_dir, 'grpc_class_init_client.rb')