UT: Rename v12 unit test fixture file to match v11

1. tests/unit/modules/dcnm/fixtures/dcnm_vrf_12.json

- Original name was dcnm_vrf.json
- Renamed to dcnm_vrf_12.json for consistency with dcnm_vrf_11.json

2. tests/unit/modules/dcnm/test_dcnm_vrf_12.py

- Update loadPlaybookData to load the new filename from 1 above.

Author: allenrobel

tests/unit/modules/dcnm/fixtures/dcnm_vrf.json renamed to tests/unit/modules/dcnm/fixtures/dcnm_vrf_12.json

@@ -30,7 +30,7 @@
 class TestDcnmVrfModule12(TestDcnmModule):
     module = dcnm_vrf
 
-    test_data = loadPlaybookData("dcnm_vrf")
+    test_data = loadPlaybookData("dcnm_vrf_12")
 
     SUCCESS_RETURN_CODE = 200