[lldb] Disable TestClangModulesUpdate.py because it's flaky

The test is failing intermittently on GreenDragon.

rdar://76540904

GitOrigin-RevId: accb0955129d94636280cbd713c905b2189e30d4
diff --git a/test/API/lang/objc/modules-update/TestClangModulesUpdate.py b/test/API/lang/objc/modules-update/TestClangModulesUpdate.py
index a24acc2..593b696 100644
--- a/test/API/lang/objc/modules-update/TestClangModulesUpdate.py
+++ b/test/API/lang/objc/modules-update/TestClangModulesUpdate.py
@@ -14,6 +14,7 @@
 
     @skipIf(debug_info=no_match(["gmodules"]))
     @skipIfReproducer # VFS is a snapshot.
+    @skipIfDarwin # rdar://76540904
     def test_expr(self):
         with open(self.getBuildArtifact("module.modulemap"), "w") as f:
             f.write("""