Bump graphql-core from 2.3.2 to 3.2.8 in /demos

Bumps [graphql-core](https://github.com/graphql-python/graphql-core) from 2.3.2 to 3.2.8.
- [Release notes](https://github.com/graphql-python/graphql-core/releases)
- [Commits](https://github.com/graphql-python/graphql-core/commits/v3.2.8)

---
updated-dependencies:
- dependency-name: graphql-core
  dependency-version: 3.2.8
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

demos/graphql-demo/requirements-dev.txt

@@ -5,7 +5,7 @@ aiodataloader==0.4.3
 faker==40.12.0
 trafaret_config==2.0.2
 graphene==2.1.9
-graphql-core==2.3.2
+graphql-core==3.2.8
 graphql-ws==0.4.4
 psycopg2-binary==2.9.11
 redis==7.4.0