chore: test on elixir 1.18

Author: fahchen

.github/workflows/elixir.yml

@@ -21,8 +21,12 @@ jobs:
       fail-fast: false
       matrix:
         include:
+          - elixir: 1.18.0
+            otp: 27.2
+          - elixir: 1.17.3
+            otp: 27.2
           - elixir: 1.16.3
-            otp: 26.2.5
+            otp: 26.2
             lint: lint
           - elixir: 1.15.6
             otp: 26.2.5