Fix broken metrics collection dialog spacing

The change around line 29-30 in
https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1368409/2/metrics_utils.py
inadvertently removed an extra space.  As a result, the metrics
collection dialog looks like this:
https://screenshot.googleplex.com/3aGtquydCXM.png

Change-Id: I7c9c08949b0df248e6de4f59ec9cfd573ff40901
Reviewed-on: https://chromium-review.googlesource.com/c/1403577
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Jared Saul <jsaul@google.com>

metrics_utils.py

@@ -27,7 +27,7 @@ EMPTY_LINE = (
 )
 NOTICE_COUNTDOWN_HEADER = (
   '┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓\n'
-  '┃  METRICS COLLECTION WILL START IN %2d EXECUTIONS  ┃'
+  '┃  METRICS COLLECTION WILL START IN %2d EXECUTIONS   ┃'
 )
 NOTICE_COLLECTION_HEADER = (
   '┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓\n'