build(deps): update asyncpg requirement

Updates the requirements on [asyncpg](https://github.com/MagicStack/asyncpg) to permit the latest version.
- [Release notes](https://github.com/MagicStack/asyncpg/releases)
- [Commits](MagicStack/asyncpg@v0.20.0...v0.29.0)

---
updated-dependencies:
- dependency-name: asyncpg
  dependency-type: direct:production
...

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

requirements.txt

@@ -1,5 +1,5 @@
 aiohttp>=3,<4
-asyncpg>=0.20,<0.28
+asyncpg>=0.20,<0.30
 beautifulsoup4>=4,<5
 commonmark>=0.8,<0.10
 dataclasses-json>=0.6.3,<0.7