Use latest OTP and Elixir versions for linting

Instead of master and main, use the latest actual release to prevent
the Dialyzer PLT from having to be regenerated every time as updates
are pushed to Elixir and Erlang.

.github/workflows/ci.yaml

@@ -11,8 +11,8 @@ jobs:
       - name: Set up Erlang and Elixir
         uses: erlef/setup-beam@v1
         with:
-          otp-version: master
-          elixir-version: main
+          otp-version: 27.x
+          elixir-version: 1.17.x
       - name: PLT cache
         uses: actions/cache@v4
         id: plt_cache