Update versions.toml (#941)

Update to the first commit where nothing in history has a bad revision:

```
 git rev-list 5c6b1a1..release-2023-11-01 | tac | xargs -I {} bash -ce 'git checkout {} && grep "smithy-lang/smithy-rs#1896" codegen-core -r'
```

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## Motivation and Context
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versions.toml

@@ -1,4 +1,4 @@
-smithy_rs_revision = '9b0e3cfd256ff737f6d23a64a323f2e526307e67'
+smithy_rs_revision = '5c6b1a19f385cc582d4795f50240394267448f9f'
 aws_doc_sdk_examples_revision = 'dc64af92d9c1780e628ab8b9f665e0490dfad6c8'
 
 [manual_interventions]