docs: replace old Rinkeby reference #14614

Job	Run time
Enable PR merge	1s
Prepare build environment	1m 1s
Check documentation	5m 29s
Build and lint Airnode	2m 2s
E2E tests (admin)	2m 46s
Require a changeset	26s
E2E tests (node)	3m 5s
Build all the Docker containers and push them to Docker Hub	6m 1s
Unit tests	6m 2s
E2E tests (utilities)	2m 7s
E2E tests (validator)	53s
E2E Tests - examples	2m 2s
All tests passed	1s
	31m 56s

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