chore: downgrade @openedx/brand-openedx to ^1.2.3

Aligns with the brand-openedx 1.x downgrade across released MFEs.
Refs openedx/public-engineering#508.

Author: arbrandes

package-lock.json

@@ -42,7 +42,7 @@
     ]
   },
   "dependencies": {
-    "@openedx/brand-openedx": "^2.0.0",
+    "@openedx/brand-openedx": "^1.2.3",
     "@openedx/frontend-app-authn": "^1.0.0-alpha || 0.0.0-dev",
     "@openedx/frontend-app-learner-dashboard": "^1.0.0-alpha || 0.0.0-dev",
     "@openedx/frontend-app-instructor-dashboard": "^1.0.0-alpha || 0.0.0-dev",