Disable supervised user creation when force sign in is enabled.

chrome/test/BUILD.gn

Index: chrome/test/BUILD.gn
diff --git a/chrome/test/BUILD.gn b/chrome/test/BUILD.gn
index 979c07c69f61623f80b5ef415fd06cc18f35aec4..293c26e6cb0fd1156ddb491c4e9fed571ae3ec34 100644
--- a/chrome/test/BUILD.gn
+++ b/chrome/test/BUILD.gn
@@ -4851,7 +4851,10 @@ test("unit_tests") {
     ]
   }
   if (enable_supervised_users && !is_android && !is_chromeos) {
-    sources += [ "../browser/ui/webui/signin/signin_supervised_user_import_handler_unittest.cc" ]
+    sources += [
+      "../browser/supervised_user/supervised_user_creation_policy_handler_unittest.cc",
+      "../browser/ui/webui/signin/signin_supervised_user_import_handler_unittest.cc",
+    ]
   }
   if (safe_browsing_mode == 1 && enable_extensions) {
     sources += [ "../browser/extensions/blacklist_unittest.cc" ]