Bump policyengine to 0.12.1

Picks up the fix for intra-decile income change double-counting
(PolicyEngine/policyengine.py#239).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: anth-volk

projects/policyengine-api-simulation/pyproject.toml

@@ -16,7 +16,7 @@ dependencies = [
     "pydantic-settings (>=2.7.1,<3.0.0)",
     "opentelemetry-instrumentation-fastapi (>=0.51b0,<0.52)",
     "policyengine-fastapi",
-    "policyengine==0.12.0",
+    "policyengine==0.12.1",
     "policyengine-core>=3.23.5",
     "policyengine-uk>=2.22.8",
     "policyengine-us>=1.370.2",