inductor_provenance: Correctly handle null provenance

Summary:
X-link: pytorch/pytorch#166019

If the provenance is null, we're getting crashes of the form
```
[trainers0]:E1021 10:51:31.990525  2752 PythonApi.h:87] Exception caught in
GeneratedDynamoCompileLoggerConfig: <class
'dsi.logger.py3.GeneratedDynamoCompile.LogEntry.thrift_types.GeneratedDynamoCompileLogEntryThriftBase'>:
error initializing Thrift struct field 'inductor_provenance_thrift_safe':
Cannot create internal string data representation. Expected type <class 'str'>,
got: <class 'NoneType'>.
```

Also fixed a type signature that wasn't being enforced. (It's still not
enforced, but it's accurate).

Reviewed By: ppanchalia

Differential Revision: D85173596

fbshipit-source-id: cccd7a8a3a840d7938083dbd7d029e761fd616b2

Author: c00w

userbenchmark/dynamo/dynamobench/_dynamo/utils.py

@@ -1377,7 +1377,7 @@ class CompilationMetrics:
     recompile_user_contexts: Optional[set[str]] = None
     inline_inbuilt_nn_modules_candidate: Optional[bool] = False
     pytorch_version: Optional[str] = None
-    inductor_provenance: Optional[str] = None
+    inductor_provenance: Optional[set[str]] = None
 
     @classmethod
     def create(cls, metrics: dict[str, Any]) -> CompilationMetrics: