GroupReindexRunnable: Fix FloggerFormatString warning

Build is failing with recent Error Prone version:

  GroupReindexRunnable.java:112: error: [FloggerFormatString]
  extra format arguments: used 0, provided 3
          log.atInfo().log("Index {}/{}/{}", g.getUUID(), g.getName(), groupLastTs.get());
                          ^
    (see https://errorprone.info/bugpattern/FloggerFormatString)

Change-Id: I654a63d7df1a156a145e6127d038b16fd411d4cb
diff --git a/src/main/java/com/ericsson/gerrit/plugins/highavailability/autoreindex/GroupReindexRunnable.java b/src/main/java/com/ericsson/gerrit/plugins/highavailability/autoreindex/GroupReindexRunnable.java
index 6331583..76c2e44 100644
--- a/src/main/java/com/ericsson/gerrit/plugins/highavailability/autoreindex/GroupReindexRunnable.java
+++ b/src/main/java/com/ericsson/gerrit/plugins/highavailability/autoreindex/GroupReindexRunnable.java
@@ -109,7 +109,7 @@
                 .max(Comparator.naturalOrder());
 
         if (groupLastTs.isPresent() && groupLastTs.get().after(sinceTs)) {
-          log.atInfo().log("Index {}/{}/{}", g.getUUID(), g.getName(), groupLastTs.get());
+          log.atInfo().log("Index %s/%s/%s", g.getUUID(), g.getName(), groupLastTs.get());
           indexer.index(g.getUUID(), Operation.INDEX, Optional.empty());
           return groupLastTs;
         }