targetRuntime function

Signed-off-by: Yves Brissaud <yves.brissaud@gmail.com>

Author: eunomie

python-sdk.dang

@@ -10,7 +10,7 @@ type PythonSdk {
   """
   Runtime source to write into modules created by this SDK.
   """
-  pub targetRuntime: String! = "python"
+  pub targetRuntime: String! { "python" }
 
   """
   Return every legacy dagger.json Dagger module whose sdk.source is "python".