[tests] change 1.2 builds to 1.3 (#7756)

script/check-size

@@ -151,9 +151,9 @@ size_nrf52840_version()
 
     local thread_version=$1
 
-    if [[ ${thread_version} == "1.2" ]]; then
+    if [[ ${thread_version} != "1.1" ]]; then
         options+=(
-            "-DOT_THREAD_VERSION=1.2"
+            "-DOT_THREAD_VERSION=1.3"
             "-DOT_BACKBONE_ROUTER=ON"
             "-DOT_DUA=ON"
             "-DOT_MLR=ON"
@@ -243,7 +243,7 @@ size_nrf52840()
     "${reporter}" init OpenThread
 
     size_nrf52840_version 1.1
-    size_nrf52840_version 1.2
+    size_nrf52840_version 1.3
 
     "${reporter}" post
 }