Fix Elixir 1.15 warnings

[axelson]

Description

Fix Elixir 1.15 warnings and a typo in the docs (caught with the in-progress elixir-lang/ex_doc#1564)

Motivation and Context

Allows users to not have to scroll through unrelated errors.

Types of changes

• Bug fix (a non-breaking change which fixes an issue)
• New feature (a non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to
  not work as expected)
• Improvement/refactoring (non-breaking change that doesn't add any feature
  but make things better)

Checklist

• Check other PRs and make sure that the changes are not done yet.