Bump asyncpg from 0.18.3 to 0.21.0 in /frameworks/Python/tornado (#7040)

Bumps [asyncpg](https://github.com/MagicStack/asyncpg) from 0.18.3 to 0.21.0.
- [Release notes](https://github.com/MagicStack/asyncpg/releases)
- [Commits](https://github.com/MagicStack/asyncpg/compare/v0.18.3...v0.21.0)

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

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

frameworks/Python/tornado/requirements_py3_uvloop.txt

@@ -1,4 +1,4 @@
-asyncpg==0.18.3
+asyncpg==0.21.0
 tornado==6.0.2
 ujson==1.35
 uvloop==0.12.1