Verify that there are no compile warnings (#330)

* Verify that there are no compile warnings

* Fix whitespace to satify the yaml gods

* Don't test elixir 1.15

Author: axelson

.github/workflows/ci.yml

@@ -46,7 +46,7 @@ jobs:
     - name: Compile Deps
       run: mix deps.compile
     - name: Compile
-      run: mix compile
+      run: mix compile --warnings-as-errors
     - name: Run Tests
       run: mix test
     - name: Run credo