Update interop repo link

Change I02ac67e333cc1a5133269bd8562f18a8d50bb036 renamed
openstack/interop to osf/interop, follow this change.

Change-Id: I43476fc0cc8f5eb2a93f75e208588f482182f3b2

Author: ajaeger

doc/source/contributor/testing.rst

@@ -123,4 +123,4 @@ Interoperability tests
 
 The DefCore committee maintains a list that contains a subset of Tempest tests.
 These are used to verify if a particular Nova deployment's API responds as
-expected. For more details, see: https://opendev.org/openstack/interop
+expected. For more details, see: https://opendev.org/osf/interop