[release-1.4] conformance: fix invalid BackendTLSPolicy conformance test (#4117)

* conformance: fix invalid BackendTLSPolicy conformance test

* Move to a real one

---------

Co-authored-by: John Howard <[email protected]>

Author: k8s-infra-cherrypick-robot

conformance/tests/backendtlspolicy-observed-generation-bump.yaml

@@ -41,5 +41,5 @@ spec:
       - group: ""
         kind: ConfigMap
         # This ConfigMap is generated dynamically by the test suite.
-        name: "backend-tls-checks-certificate"
+        name: "tls-checks-ca-certificate"
     hostname: "abc.example.com"