manifest: pin to Zephyr v2.6.0

Pin to Zephyr v2.6.0 for the v2.6.0 release of the example-application.

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>

Author: gmarull

west.yml

@@ -12,5 +12,5 @@ manifest:
   projects:
     - name: zephyr
       remote: zephyrproject-rtos
-      revision: main
+      revision: v2.6.0
       import: true