test: Add missing tests for `traffic_switcher.go` (#17334) #504

Job	Run time
Build and push vttestserver (mysql80)	2m 25s
Build and push lite (latest)	4m 55s
Build and push lite (percona80)	4m 38s
Build and push (bullseye, vtadmin)	1m 28s
Build and push (bullseye, vtorc)	46s
Build and push (bullseye, vtgate)	50s
Build and push (bullseye, vttablet)	55s
Build and push (bullseye, mysqlctld)	46s
Build and push (bullseye, mysqlctl)	42s
Build and push (bullseye, vtctl)	47s
Build and push (bullseye, vtctlclient)	46s
Build and push (bullseye, vtctld)	1m 35s
Build and push (bullseye, vtctldclient)	45s
Build and push (bullseye, logrotate)	26s
Build and push (bullseye, logtail)	28s
Build and push (bullseye, vtbackup)	48s
Build and push (bullseye, vtexplain)	50s
Build and push (bookworm, vtadmin)	1m 34s
Build and push (bookworm, vtorc)	50s
Build and push (bookworm, vtgate)	49s
Build and push (bookworm, vttablet)	47s
Build and push (bookworm, mysqlctld)	49s
Build and push (bookworm, mysqlctl)	53s
Build and push (bookworm, vtctl)	49s
Build and push (bookworm, vtctlclient)	38s
Build and push (bookworm, vtctld)	1m 44s
Build and push (bookworm, vtctldclient)	57s
Build and push (bookworm, logrotate)	37s
Build and push (bookworm, logtail)	35s
Build and push (bookworm, vtbackup)	56s
Build and push (bookworm, vtexplain)	50s
Slack Notification if failed	0s
	36m 38s

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