NAS-132591 / Update 13.3 build to use the proper iocage branch (#322)

There have been no iocage changes since 13.0 and so we can just
use truenas/13.0-stable for our iocage branch.

build/profiles/freenas/repos.pyd

@@ -77,5 +77,5 @@ repos += {
     "name": "iocage",
     "path": "iocage",
     "url": "https://github.com/freenas/iocage.git",
-    "branch": "truenas/12.0-stable"
+    "branch": "truenas/13.0-stable"
 }