change: rename from `experimental-islands` to `islands` #2806

Job	Run time
get-example-changed / Get Example Changed	5s
get-matrix / Get Changed Example Matrix	9s
CI (examples/hackernews_islands_axum) / Run ci (stable)	7m 13s
CI (examples/islands_router) / Run ci (stable)	3m 27s
CI (examples/islands) / Run ci (stable)	3m 33s
	14m 27s

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