Fix calculating -otp- major for Elixir (#351)

* Set expectations

* Ease testing without having to install via `require`

* Code a solution for the tests

* Avoid errors on unit tests

rebar3 is saying something about SSL, most likely because
our tests are installing a bunch of OTPs which makes
for unpredictable behavior

* Avoid errors on integration tests

.github/workflows/action.yml

@@ -76,6 +76,7 @@ jobs:
         uses: ./
         with:
           install-rebar: false
+          install-hex: false
           version-file: test/.tool-versions
           version-type: strict