chg: [CI] remove older elixir versions

.github/workflows/test.yml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       matrix:
         otp: ["24.x"]
-        elixir: ["1.12.3", "1.13.3", "1.14.3", "1.15.3", "1.16.3"]
+        elixir: ["1.16.3"]
     steps:
       - uses: actions/checkout@v3