chore(deps): Update pygments requirement from ~=2.19 to ~=2.20 in /demo

Updates the requirements on [pygments](https://github.com/pygments/pygments) to permit the latest version.
- [Release notes](https://github.com/pygments/pygments/releases)
- [Changelog](https://github.com/pygments/pygments/blob/master/CHANGES)
- [Commits](pygments/pygments@2.19.0...2.20.0)

---
updated-dependencies:
- dependency-name: pygments
  dependency-version: 2.20.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

demo/requirements.txt

@@ -1,4 +1,4 @@
 asyncpg~=0.31.0
 prompt_toolkit~=3.0.51
-pygments~=2.19
+pygments~=2.20
 qrcode[pil]~=8.2