Enable BraveWorkaroundNewWindowFlash 25% Release (#1213)

1.70.x is now Release, so we can continue rolling this feature. It's
already enabled by default in Nightly and Beta.

Related #1178

seed/seed.json

@@ -2861,7 +2861,7 @@
  ]
  },
  "name": "Enabled",
- "probability_weight": 0
+ "probability_weight": 25
  },
  {
  "feature_association": {
@@ -2870,7 +2870,7 @@
  ]
  },
  "name": "Disabled",
- "probability_weight": 100
+ "probability_weight": 75
  },
  {
  "name": "Default",