Add pip as a host dependency.

The build succeeds without that, but the `script` line does utilize pip so I suppose it is technically needed.

Co-authored-by: Uwe L. Korn <xhochy@users.noreply.github.com>

recipes/odl/meta.yaml

@@ -17,6 +17,7 @@ build:
 requirements:
   host:
     - python >=3.7
+    - pip
     - setuptools >=65.6
 
   run: