test: add tests for RetryConfigMapping

Author: schiemon

core/src/main/java/com/linecorp/armeria/client/retry/RetryConfigMappingBuilder.java

@@ -42,7 +42,7 @@ private boolean validateMappingKeys() {
         return perHost || perMethod || perPath;
     }
 
-    public RetryConfigMapping<T> build(RetryConfigFactory retryConfigFactory) {
+    public RetryConfigMapping<T> build(RetryConfigFactory<T> retryConfigFactory) {
         if (!validateMappingKeys()) {
             throw new IllegalStateException(
                     "A RetryConfigMapping created by this builder must be per host, method and/or path");