Add Elixir 1.20 to test matrix

Author: adam12

.github/workflows/main.yml

@@ -6,7 +6,7 @@ jobs:
   test:
     strategy:
       matrix:
-        elixir_version: [1.17, 1.16, 1.15, 1.14, 1.13]
+        elixir_version: [1.20, 1.17, 1.16, 1.15, 1.14, 1.13]
     runs-on: ubuntu-latest
     container:
       image: elixir:${{ matrix.elixir_version }}