Update azure-functions requirement in /code/function

Updates the requirements on [azure-functions](https://github.com/Azure/azure-functions-python-worker) to permit the latest version.
- [Release notes](https://github.com/Azure/azure-functions-python-worker/releases)
- [Commits](https://github.com/Azure/azure-functions-python-worker/commits)

---
updated-dependencies:
- dependency-name: azure-functions
  dependency-type: direct:production
...

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Author: dependabot[bot]

code/function/requirements.txt

@@ -3,7 +3,7 @@
 # Manually managing azure-functions-worker may cause unexpected issues
 
 # azure-identity~=1.13.0
-azure-functions~=1.14.0
+azure-functions~=1.15.0
 fastapi~=0.96.1
 aiohttp~=3.8.4
 opentelemetry-instrumentation-fastapi==0.39b0