update CI to include new Elixir and OTP versions

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Summary

Updates CI to include a bunch more Elixir and Erlang versions.

Note that the Elixir 1.12 tests are currently failing and will be fixed once https://github.com/witchcrafters/witchcraft/pull/86 is merged.

This PR fixes/implements the following bugs/features

Explain the motivation for making this change. What existing problem does the pull request solve?

This will make it easier to see if a change breaks in some version of Elixir or Erlang.

Demonstrate the code is solid. Example: The exact commands you ran and their output, screenshots / videos if the pull request changes UI.

Fixes #

[ ] Does this change invalidate any docs or tutorials? If so ensure the changes needed are either made or recorded
[ ] Does this change require a release to be made? Is so please create and deploy the release