Update to Elixir 1.20.1 and refresh Hex packages.

[conradwt]

This PR supports the following features:

• update to Elixir 1.20.1
• refresh Hex packages

[github-actions]

Docker image tag(s) pushed:

ghcr.io/conradwt/zero-to-graphql-using-elixir:gha-27330136455
ghcr.io/conradwt/zero-to-graphql-using-elixir:pr-316 

Labels added to images:

org.opencontainers.image.created=2026-06-11T07:10:45.939Z
org.opencontainers.image.description=The purpose of this example is to provide details as to how one would go about using GraphQL with the Elixir Language.
org.opencontainers.image.licenses=MIT
org.opencontainers.image.revision=0242795b0899be78e29608f824df4f37522041aa
org.opencontainers.image.source=https://github.com/conradwt/zero-to-graphql-using-elixir
org.opencontainers.image.title=zero-to-graphql-using-elixir
org.opencontainers.image.url=https://github.com/conradwt/zero-to-graphql-using-elixir
org.opencontainers.image.version=gha-27330136455