Quick Answers: Update field trial params for translation

Bug: b/175747630
Test: None
Change-Id: I48729ab6e3105a829f1338517cb1796bd70a8e65
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2612517
Auto-Submit: Yue Li <updowndota@chromium.org>
Commit-Queue: Mark Pearson <mpearson@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#840678}

testing/variations/fieldtrial_testing_config.json

@@ -6179,7 +6179,7 @@
                 {
                     "name": "Enabled",
                     "params": {
-                        "selected_text_confidence_threshold": "0.7",
+                        "selected_text_confidence_threshold": "0.8",
                         "surrounding_text_confidence_threshold": "0.9"
                     },
                     "enable_features": [