Update PasswordCheck study experiment name for 20% rollout

Bug: 1032584
Change-Id: Ieb33f3d457c86071ebb72b26e35281a26e27314d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2214548
Commit-Queue: Sean Harrison <harrisonsean@chromium.org>
Commit-Queue: Alexei Svitkine <asvitkine@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#774741}

testing/variations/fieldtrial_testing_config.json

@@ -4409,7 +4409,7 @@
             ],
             "experiments": [
                 {
-                    "name": "WithEnhancedExperiment_20200519",
+                    "name": "WithEnhancedExperiment_20200603",
                     "params": {
                         "DefaultInIncognito": "true"
                     },