Bump aiohttp from 3.11.18 to 3.12.15 in /demos (#1565)

---
updated-dependencies:
- dependency-name: aiohttp
  dependency-version: 3.12.15
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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demos/blog/requirements.txt

@@ -1,4 +1,4 @@
-aiohttp==3.11.18
+aiohttp==3.12.15
 aiohttp-jinja2==1.6
 aiohttp-security[session]==0.5.0
 asyncpg==0.30.0

demos/polls/requirements-dev.txt

@@ -1,4 +1,4 @@
-aiohttp==3.11.18
+aiohttp==3.12.15
 aiohttp-jinja2==1.6
 asyncpg==0.30.0
 trafaret_config==2.0.2