[minor] Prefer signal.NotifyContext to signal.Notify in kanx (#3180) #7088

Job	Run time
gomod	51s
image_tags	1s
docs	29s
lint	3m 28s
test (test)	10m 58s
reno_lint	40s
test (integration-test)	7m 40s
build (controller)	2m 26s
test (helm-test)	2m 55s
build (kanctl)	2m 24s
build (kando)	2m 12s
release	10m 40s
release_example_docker_images / build_cassandra / build_image	56s
release_example_docker_images / build_kafka-adobe-s3-sink-connector / build_image	7m 36s
release_example_docker_images / build_kafka-adobe-s3-source-connector / build_image	7m 35s
release_example_docker_images / build_es-sidecar / build_image	7m 39s
release_example_docker_images / build_mongodb / build_image	55s
release_example_docker_images / build_mssql-tools / build_image	30s
release_example_docker_images / build_mysql_sidecar / build_image	2m 31s
release_example_docker_images / build_postgres-kanister-tools / build_image	5m 22s
release_example_docker_images / build_postgresql / build_image	5m 33s
	1h 23m 21s

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