elixir.yml: More consistent case

When running this action, it will show steps like "Set up job", "Initialize containers" and "Complete job", which are not in Title Case. Nor is "Set up Elixir".

(Some steps like "Post Restore cache" are some sort of half-Title Case, but they seem to be in the minority.)

ci/elixir.yml

@@ -18,7 +18,7 @@ jobs:
       with:
         elixir-version: '1.9.4' # Define the elixir version [required]
         otp-version: '22.2' # Define the OTP version [required]
-    - name: Install Dependencies
+    - name: Install dependencies
       run: mix deps.get
-    - name: Run Tests
+    - name: Run tests
       run: mix test