Make TestRateLimiter locale-independent (#469)

The vendored Guava test formatted expected events with the default
locale, so it failed on JVMs using a comma decimal separator.

Assisted-By: Claude Fable 5 <noreply@anthropic.com>

Author: ppkarwasz

flume-ng-core/src/test/java/org/apache/flume/source/shaded/guava/TestRateLimiter.java

@@ -23,6 +23,7 @@
 import com.google.common.collect.Lists;
 import java.util.Arrays;
 import java.util.List;
+import java.util.Locale;
 import java.util.Random;
 import junit.framework.TestCase;
 import org.apache.flume.source.shaded.guava.RateLimiter.SleepingStopwatch;
@@ -428,7 +429,7 @@ void sleepMillis(int millis) {
 
         void sleepMicros(String caption, long micros) {
             instant += MICROSECONDS.toNanos(micros);
-            events.add(caption + String.format("%3.2f", (micros / 1000000.0)));
+            events.add(caption + String.format(Locale.ROOT, "%3.2f", (micros / 1000000.0)));
         }
 
         @Override