fix: examples/pubnub_asyncio/fastapi/requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-AIOHTTP-6091621
- https://snyk.io/vuln/SNYK-PYTHON-AIOHTTP-6091622
- https://snyk.io/vuln/SNYK-PYTHON-AIOHTTP-6209406
- https://snyk.io/vuln/SNYK-PYTHON-AIOHTTP-6209407
- https://snyk.io/vuln/SNYK-PYTHON-AIOHTTP-6645291
- https://snyk.io/vuln/SNYK-PYTHON-AIOHTTP-6808823
- https://snyk.io/vuln/SNYK-PYTHON-AIOHTTP-7675597
- https://snyk.io/vuln/SNYK-PYTHON-AIOHTTP-8383923
- https://snyk.io/vuln/SNYK-PYTHON-REQUESTS-6928867
- https://snyk.io/vuln/SNYK-PYTHON-URLLIB3-7267250
- https://snyk.io/vuln/SNYK-PYTHON-ZIPP-7430899

Author: snyk-bot

examples/pubnub_asyncio/fastapi/requirements.txt

@@ -1,2 +1,6 @@
 fastapi>=0.115.11
-pubnub>=10.1.0
+pubnub>=10.1.0
+aiohttp>=3.10.11 # not directly required, pinned by Snyk to avoid a vulnerability
+requests>=2.32.2 # not directly required, pinned by Snyk to avoid a vulnerability
+urllib3>=2.2.2 # not directly required, pinned by Snyk to avoid a vulnerability
+zipp>=3.19.1 # not directly required, pinned by Snyk to avoid a vulnerability