Add CEL validation test for `targetRef` in ClientSettingsPolicy #14085

Job	Run time
Checks and variables	1m 47s
Unit Tests	1m 8s
NJS Unit Tests	10s
Build Binary	28s
Build Plus images / build	1m 10s
Build OSS images (ngf, linux/arm64, linux/amd64) / build	1m 8s
Build OSS images (nginx, linux/arm64, linux/amd64) / build	1m 12s
Helm Tests	0s
Functional tests (nginx, v1.25.16) / Run Tests	12m 53s
Functional tests (plus, v1.25.16) / Run Tests	11m 21s
Functional tests (nginx, v1.33.1) / Run Tests	12m 6s
Conformance tests (nginx, v1.33.1, true) / Run Tests	6m 47s
Conformance tests (nginx, v1.25.16, false) / Run Tests	7m 33s
Conformance tests (plus, v1.33.1, true) / Run Tests	7m 42s
Conformance tests (plus, v1.25.16, true) / Run Tests	8m 45s
Conformance tests (nginx, v1.33.1, false) / Run Tests	6m 47s
Conformance tests (plus, v1.33.1, false) / Run Tests	7m 12s
Conformance tests (nginx, v1.25.16, true) / Run Tests	8m 12s
Conformance tests (plus, v1.25.16, false) / Run Tests	7m 45s
Functional tests (plus, v1.33.1) / Run Tests	10m 36s
Package and Publish Helm Chart	0s
	1h 54m 42s

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