Correct experiment group name for SmartDimModelV3

Bug: 937063
Change-Id: I836d350cf492549f2c4f8590876d0170c5dbe1d7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2048044
Auto-Submit: Andrew Moylan <amoylan@chromium.org>
Commit-Queue: Steven Holte <holte@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Cr-Commit-Position: refs/heads/master@{#740393}

testing/variations/fieldtrial_testing_config.json

@@ -6344,7 +6344,7 @@
             ],
             "experiments": [
                 {
-                    "name": "Enabled",
+                    "name": "Enabled_20200207",
                     "params": {
                         "dim_threshold": "-0.5"
                     },