improve: informer health check should not rely on isWatching #6339

Job	Run time
check_format_and_unit_tests	1m 28s
build / Special integration tests (17)	2m 25s
build / Special integration tests (21)	2m 31s
build / Special integration tests (25)	2m 30s
build / httpclient-tests (jdk) / Integration tests (25, 1.32.0, jdk)	26m 54s
build / integration_tests (21, 1.31.8) / Integration tests (21, 1.31.8, vertx)	28m 7s
build / httpclient-tests (jetty) / Integration tests (25, 1.32.0, jetty)	26m 39s
build / httpclient-tests (vertx) / Integration tests (25, 1.32.0, vertx)	26m 53s
build / integration_tests (25, 1.33.1) / Integration tests (25, 1.33.1, vertx)	27m 16s
build / integration_tests (25, 1.32.4) / Integration tests (25, 1.32.4, vertx)	25m 59s
build / integration_tests (17, 1.33.1) / Integration tests (17, 1.33.1, vertx)	28m 18s
build / integration_tests (17, 1.32.4) / Integration tests (17, 1.32.4, vertx)	26m 35s
build / integration_tests (21, 1.30.12) / Integration tests (21, 1.30.12, vertx)	26m 41s
build / integration_tests (21, 1.32.4) / Integration tests (21, 1.32.4, vertx)	28m 7s
build / integration_tests (25, 1.30.12) / Integration tests (25, 1.30.12, vertx)	25m 49s
build / integration_tests (17, 1.30.12) / Integration tests (17, 1.30.12, vertx)	26m 25s
build / integration_tests (17, 1.31.8) / Integration tests (17, 1.31.8, vertx)	27m 50s
build / integration_tests (25, 1.31.8) / Integration tests (25, 1.31.8, vertx)	28m 23s
build / integration_tests (21, 1.33.1) / Integration tests (21, 1.33.1, vertx)	28m 53s
	6h 57m 43s

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