Update CI to use Elixir 1.13.4/OTP 25.2

Author: paulgoetze

.github/workflows/elixir.yml

@@ -10,13 +10,20 @@ jobs:
   build:
     runs-on: ubuntu-latest
 
+    name: Test on OTP ${{matrix.otp}} / Elixir ${{matrix.elixir}}
+    strategy:
+      # Specify the OTP and Elixir versions to use when building
+      # and running the workflow steps.
+      matrix:
+        otp: ['25.2.0']       # Define the OTP version [required]
+        elixir: ['1.13.4']    # Define the elixir version [required]
     steps:
-    - uses: actions/checkout@v2
-    - name: Setup elixir
-      uses: actions/setup-elixir@v1
+    # Step: Setup Elixir + Erlang image as the base.
+    - name: Set up Elixir
+      uses: erlef/setup-beam@v1
       with:
-        elixir-version: 1.9.4 # Define the elixir version [required]
-        otp-version: 22.2 # Define the OTP version [required]
+        otp-version: ${{matrix.otp}}
+        elixir-version: ${{matrix.elixir}}
     - name: Check formatting
       run: mix format --check-formatted