Update Elixir version to 1.18.4-otp-27 in CI configuration

Author: solnic

.github/workflows/main.yml

@@ -22,7 +22,7 @@ jobs:
         # https://hexdocs.pm/elixir/compatibility-and-deprecations.html#compatibility-between-elixir-and-erlang-otp
         include:
           # Newest supported Elixir/Erlang pair.
-          - elixir: '1.18.4'
+          - elixir: '1.18.4-otp-27'
             otp: '28.0'
             lint: true
             dialyzer: true