Switch e2e testing assertions to use EndpointSlices #11647

Job	Run time
style / changes	4s
style / Golang / Auto-format and Check	23s
style / Golang / Do Not Submit	7s
style / Golang / Lint	3m 50s
style / Golang / Boilerplate Check (go)	24s
style / Golang / Boilerplate Check (sh)	21s
style / suggester / github_actions	0s
style / suggester / yaml	0s
style / suggester / shell	0s
	5m 9s

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