[minor] Prefer signal.NotifyContext to signal.Notify in kanx #7087

Job	Run time
gomod	1m 2s
image_tags	1s
docs	32s
reno_lint	42s
test (test)	11m 27s
lint	3m 36s
test (integration-test)	8m 8s
build (controller)	2m 30s
test (helm-test)	3m 17s
build (kanctl)	2m 23s
build (kando)	2m 17s
release	0s
release_example_docker_images	0s
	35m 55s

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