Bump asyncpg from 0.30.0 to 0.31.0 in /demos

Bumps [asyncpg](https://github.com/MagicStack/asyncpg) from 0.30.0 to 0.31.0.
- [Release notes](https://github.com/MagicStack/asyncpg/releases)
- [Commits](MagicStack/asyncpg@v0.30.0...v0.31.0)

---
updated-dependencies:
- dependency-name: asyncpg
  dependency-version: 0.31.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

demos/blog/requirements.txt

@@ -1,7 +1,7 @@
 aiohttp==3.13.2
 aiohttp-jinja2==1.6
 aiohttp-security[session]==0.5.0
-asyncpg==0.30.0
+asyncpg==0.31.0
 bcrypt==5.0.0
 pytoml==0.1.21
 redis==7.1.0

demos/polls/requirements-dev.txt

@@ -1,6 +1,6 @@
 aiohttp==3.13.2
 aiohttp-jinja2==1.6
-asyncpg==0.30.0
+asyncpg==0.31.0
 trafaret_config==2.0.2
 SQLalchemy==2.0.44