TaskTree: fix errorprone warning about Flogger

See https://errorprone.info/bugpattern/FloggerLogString for details.

Change-Id: I8e50b7d1a039d1004a5751b275972de877466f7f

src/main/java/com/googlesource/gerrit/plugins/task/TaskTree.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/task/TaskTree.java b/src/main/java/com/googlesource/gerrit/plugins/task/TaskTree.java
index 9c4b476..cb7e2d4 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/task/TaskTree.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/task/TaskTree.java
@@ -261,7 +261,7 @@
           return;
         }
       } catch (StorageException e) {
-        log.atSevere().withCause(e).log("ERROR: running changes query: " + namesFactory.changes);
+        log.atSevere().withCause(e).log("ERROR: running changes query: %s", namesFactory.changes);
       } catch (QueryParseException e) {
       }
       addSubDefinition(null);