my_activity.py: add coreboot gerrit

Add review.coreboot.org to the list of gerrit repos that
my_activity.py will query to find CLs.

Change-Id: I2c78c3365ee77f6a99ca6a39deda08bb913be5c2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2350325
Reviewed-by: Dirk Pranke <dpranke@google.com>
Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Dirk Pranke <dpranke@google.com>

my_activity.py

@@ -100,6 +100,9 @@ gerrit_instances = [
   {
     'url': 'skia-review.googlesource.com',
   },
+  {
+    'url': 'review.coreboot.org',
+  },
 ]
 
 monorail_projects = {