Skip tests in TestThreadLockNativeThread when using LSAN

These tests use NM threads but NT is not freed for MN thread, causing it
to be reported as memory leaks in LSAN. For example:

    #1 0x62ee7bc67e99 in calloc1 gc/default/default.c:1495:12
    #2 0x62ee7bc7ba00 in rb_gc_impl_calloc gc/default/default.c:8216:5
    #3 0x62ee7bc631d1 in ruby_xcalloc_body gc.c:5221:12
    #4 0x62ee7bc5cdbc in ruby_xcalloc gc.c:5215:34
    #5 0x62ee7bdea4c6 in native_thread_alloc thread_pthread.c:2187:35
    #6 0x62ee7bdec31b in native_thread_check_and_create_shared thread_pthread_mn.c:429:39
    #7 0x62ee7bdea484 in native_thread_create_shared thread_pthread_mn.c:531:12
    #8 0x62ee7bdea1da in native_thread_create thread_pthread.c:2403:16
    #9 0x62ee7bdde2eb in thread_create_core thread.c:884:11
    #10 0x62ee7bde4466 in thread_initialize thread.c:992:16

Author: peterzhu2118

test/-ext-/thread/test_lock_native_thread.rb

@@ -15,6 +15,8 @@
 
 class TestThreadLockNativeThread < Test::Unit::TestCase
   def test_lock_native_thread
+    omit "LSAN reports memory leak because NT is not freed for MN thread" if Test::Sanitizers.lsan_enabled?
+
     assert_separately([{'RUBY_MN_THREADS' => '1'}], <<-RUBY)
       require '-test-/thread/lock_native_thread'
 
@@ -28,6 +30,8 @@ def test_lock_native_thread
   end
 
   def test_lock_native_thread_tls
+    omit "LSAN reports memory leak because NT is not freed for MN thread" if Test::Sanitizers.lsan_enabled?
+
     assert_separately([{'RUBY_MN_THREADS' => '1'}], <<-RUBY)
       require '-test-/thread/lock_native_thread'
       tn = 10