Switch from Force Tags to Test Tags

Force Tags is deprecated in Robot 7.0 and will eventually
warn and then after that stop working. Test Tags performs
the same function per docs.

Change-Id: I7cf305754b247b995a05d8da3b9de9ed613ecae2
Signed-off-by: Matt Fischer <matthew.fischer@hpe.com>
diff --git a/redfish/managers/test_certificate.robot b/redfish/managers/test_certificate.robot
index e71a33a..db064ec 100644
--- a/redfish/managers/test_certificate.robot
+++ b/redfish/managers/test_certificate.robot
@@ -7,7 +7,7 @@
 Resource         ../../lib/certificate_utils.robot
 Library          String
 
-Force Tags       Certificate
+Test Tags       Certificate
 
 Suite Setup      Suite Setup Execution
 Suite Teardown   Suite Teardown