Add missing 139 relnotes in TOC (#3493)

Author: captainbrosset

microsoft-edge/toc.yml

@@ -30,9 +30,13 @@
           href: ./web-platform/release-notes/index.md
           displayName: what's new, announcements
 
+        - name: Microsoft Edge 139
+          href: ./web-platform/release-notes/139.md
+          displayName: Microsoft Edge 139 web platform release notes (Aug. 2025)  # page title
+
         - name: Microsoft Edge 138
           href: ./web-platform/release-notes/138.md
-          displayName: Microsoft Edge 137 web platform release notes (Jun. 2025)  # page title
+          displayName: Microsoft Edge 138 web platform release notes (Jun. 2025)  # page title
 
         - name: Microsoft Edge 137
           href: ./web-platform/release-notes/137.md