Update enable-force-dark flag expiration to M90

Bug: 1100139
Change-Id: Iffcd8b2148cea9fa295ae2f93c45ec4774087c77
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2273500
Commit-Queue: Philip Rogers <pdr@chromium.org>
Reviewed-by: Theresa  <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#783659}

chrome/browser/flag-metadata.json

@@ -1641,8 +1641,8 @@
   },
   {
     "name": "enable-force-dark",
-    "owners": [ "gilmanmh@google.com" ],
-    "expiry_milestone": 85
+    "owners": [ "pdr" ],
+    "expiry_milestone": 90
   },
   {
     "name": "enable-fs-nosymfollow",