Bump pygments from 2.19.1 to 2.20.0 in /demos/a2a_llama_stack

Bumps [pygments](https://github.com/pygments/pygments) from 2.19.1 to 2.20.0.
- [Release notes](https://github.com/pygments/pygments/releases)
- [Changelog](https://github.com/pygments/pygments/blob/master/CHANGES)
- [Commits](pygments/pygments@2.19.1...2.20.0)

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

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

Author: dependabot[bot]

demos/a2a_llama_stack/requirements.txt

@@ -46,7 +46,7 @@ pyaml==25.1.0
 pycparser==2.22
 pydantic==2.11.3
 pydantic_core==2.33.1
-Pygments==2.19.1
+Pygments==2.20.0
 PyJWT==2.10.1
 python-dateutil==2.9.0.post0
 python-dotenv==1.1.0