Fix TranslogTests#testStats (#66227)

If creating the latest translog file and retrieving a translog stats
happen within the same millisecond, then the earliestLastModifiedAge
will be zero.

Closes #66092

server/src/test/java/org/elasticsearch/index/translog/TranslogTests.java

@@ -507,6 +507,7 @@ public void testStats() throws IOException {
 
         markCurrentGenAsCommitted(translog);
         {
+            lastModifiedAge = System.currentTimeMillis() - translog.getCurrent().getLastModifiedTime();
             final TranslogStats stats = stats();
             assertThat(stats.estimatedNumberOfOperations(), equalTo(4));
             assertThat(stats.getTranslogSizeInBytes(), equalTo(expectedSizeInBytes));