Narrow test_crud_instance moto-skip to ==5.2.1

The skip specifier was `>=5.0.0`, which silently masks the test for
every future moto release. Pin to the exact known-broken version
(5.2.1) so newer releases re-run the test — we want to discover an
upstream fix the first time CI installs a newer moto, not stay quiet
forever.

tests/test_compute_service.py

@@ -35,11 +35,12 @@ class CloudComputeServiceTestCase(ProviderTestBase):
     # immediately after RunInstances completes, so the list-after-create
     # check in standard_interface_tests.check_list fails. A secondary
     # symptom shows in cleanup, where post-delete state remains
-    # "deleted" instead of becoming UNKNOWN. Last observed on moto
-    # 5.2.1. Tighten the specifier when an upstream fix lands.
+    # "deleted" instead of becoming UNKNOWN. Pinned to the latest moto
+    # release where this was observed (5.2.1); newer releases re-run the
+    # test so we notice if it's fixed. Bump the pin if it's still broken.
     @helpers.skipIfMockMotoVersion(
-        ">=5.0.0",
-        "moto 5.x RunInstances/DescribeInstances state-sync bug")
+        "==5.2.1",
+        "moto 5.2.1 RunInstances/DescribeInstances state-sync bug")
     @helpers.skipIfNoService(['compute.instances', 'networking.networks'])
     def test_crud_instance(self):
         label = "cb-instcrud-{0}".format(helpers.get_uuid())