sets a fixed version for pixman when buildign desktop client via Craft

Signed-off-by: Matthieu Gallien <matthieu.gallien@nextcloud.com>

craftmaster.ini

@@ -49,6 +49,7 @@ dev-utils/python2.ignored = True
 dev-utils/python3.ignored = True
 nextcloud-client.buildTests = True
 binary/mysql.useMariaDB = False
+libs/pixman.version = 0.40.0
 
 [windows-msvc2019_64-cl]
 QtSDK/Compiler = msvc2019_64