releng: move to a non-official release

This is required for releng to cut a new release.

This is suboptimal releng as the script should probably do it itself and
merge the releng branch.

As we are in a hurry, we will skip this.

Change-Id: I54fccb11938adefc8685d04247e16401135dad8d
Signed-off-by: Raito Bezarius <raito@lix.systems>

version.json

@@ -1,5 +1,5 @@
 {
     "version": "2.91.2",
-    "official_release": true,
+    "official_release": false,
     "release_name": "Dragon's Breath"
 }