sync.profile: Point dependencies to 'refs/heads/stable'

We should test stable branches against stable branches only.
At some point we should automate the merges from dev->stable->release
and decide how to handle possible merge conflicts.

This is good enough for the time being.

Change-Id: Ie117ec0e488c740c0be01359912520d54c24248f
Reviewed-by: Janne Anttila <janne.anttila@digia.com>

sync.profile

@@ -10,5 +10,5 @@
 #   - any git symbolic ref resolvable from the module's repository (e.g. "refs/heads/master" to track master branch)
 #
 %dependencies = (
-    "qtbase" => "refs/heads/master",
+    "qtbase" => "refs/heads/stable",
 );