Update version number.

Author: jonsimantov

cpp_sdk_version.json

@@ -1,5 +1,5 @@
 {
-  "released": "12.5.0",
-  "stable": "12.5.0",
-  "head": "12.5.0"
+  "released": "12.6.0",
+  "stable": "12.6.0",
+  "head": "12.6.0"
 }

release_build_files/readme.md

@@ -631,6 +631,11 @@ workflow use only during the development of your app, not for publicly shipping
 code.
 
 ## Release Notes
+### 12.6.0
+-   Changes
+    - General (iOS): Update to Firebase Cocoapods version 11.8.1.
+    - General (Android): Update to Firebase Android BoM version 33.9.0.
+
 ### 12.5.0
 -   Changes
     - General (iOS): Update to Firebase Cocoapods version 11.6.0.