gh-122320: Limit dict key versions used by test_opcache. (gh-132961)

The `test_load_global_module()` test consumes a lot of dict key versions.
Skip the test if we have consumed half of the available versions that can be
used for the "load global" cache.

Lib/test/test_opcache.py

@@ -16,6 +16,16 @@ if check_impl_detail(cpython=False):
 _testinternalcapi = import_module("_testinternalcapi")
 
 
+def have_dict_key_versions():
+    # max version value that can be stored in the load global cache. This is
+    # determined by the type of module_keys_version and builtin_keys_version
+    # in _PyLoadGlobalCache, uint16_t.
+    max_version = 1<<16
+    # use a wide safety margin (use only half of what's available)
+    limit = max_version // 2
+    return _testinternalcapi.get_next_dict_keys_version() < limit
+
+
 class TestBase(unittest.TestCase):
     def assert_specialized(self, f, opname):
         instructions = dis.get_instructions(f, adaptive=True)
@@ -1029,6 +1039,8 @@ class TestRacesDoNotCrash(TestBase):
 
     @requires_specialization_ft
     def test_load_global_module(self):
+        if not have_dict_key_versions():
+            raise unittest.SkipTest("Low on dict key versions")
         def get_items():
             items = []
             for _ in range(self.ITEMS):