Review fixes for logback-appender-1.0:testing (open-telemetry#17529)

Co-authored-by: otelbot <197425009+otelbot@users.noreply.github.com>

Author: otelbot[bot]

instrumentation/logback/logback-appender-1.0/testing/src/main/java/io/opentelemetry/instrumentation/logback/appender/v1_0/AbstractLogbackTest.java

@@ -303,12 +303,12 @@ private static void performLogging(
   }
 
   @FunctionalInterface
-  public interface OneArgLoggerMethod {
+  private interface OneArgLoggerMethod {
     void call(Logger logger, String msg, Object arg);
   }
 
   @FunctionalInterface
-  public interface TwoArgLoggerMethod {
+  private interface TwoArgLoggerMethod {
     void call(Logger logger, String msg, Object arg1, Object arg2);
   }
 }