fix CI test name

Author: Yejun Su

.github/workflows/main.yml

@@ -5,7 +5,7 @@ on: [push, pull_request]
 jobs:
   tests:
     runs-on: ubuntu-latest
-    name: OTP ${{matrix.otp}} / Elixir ${{matrix.elixir}}
+    name: OTP ${{matrix.pair.otp}} / Elixir ${{matrix.pair.elixir}}
     strategy:
       matrix:
         pair: