Update to Erlang 28.0.1.

[conradwt]

This PR supports the following features:

• update to Erlang 28.0.1
• update Hex packages
• update system requirements

[github-actions]

Docker image tag(s) pushed:

ghcr.io/conradwt/zero-to-graphql-using-elixir:gha-15768585221
ghcr.io/conradwt/zero-to-graphql-using-elixir:pr-270 

Labels added to images:

org.opencontainers.image.created=2025-06-20T00:34:58.005Z
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=034fe1d62bc941dc5bed289456c234cf657f3146
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-15768585221