[MLIR][Python] fix StandalonePythonModules shipping all dialect modules

[makslevental]

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darker --check --diff -r origin/main...HEAD mlir/examples/standalone/test/python/smoketest.py

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--- smoketest.py	2025-08-28 16:16:38.000000 +0000
+++ smoketest.py	2025-08-28 16:18:41.396788 +0000
@@ -28,8 +28,11 @@
 from mlir_standalone.dialects import quant
 
 try:
     from mlir_standalone.dialects import quant
 except ImportError as e:
-    assert "symbol not found in flat namespace '_mlirTypeIsAAnyQuantizedType'" not in e.args[0]
+    assert (
+        "symbol not found in flat namespace '_mlirTypeIsAAnyQuantizedType'"
+        not in e.args[0]
+    )
 else:
     assert False, "expected exception not raised"