fix(tests): Guarantee that TripPlannerTest headsigns are different from each other #5532

Job	Run time
Build application and assets	6m 21s
file_changes	6s
Build Docker image	7m 16s
Linting / TypeScript	47s
Linting / Elixir	3m 25s
Linting / CSS	22s
Linting / JavaScript	30s
Formatting / JavaScript & TypeScript	27s
Formatting / Elixir	3m 14s
Unit tests / JavaScript / Mocha	46s
Unit tests / JavaScript & TypeScript / Jest	2m 17s
Type checks / Elixir	3m 47s
Type checks / TypeScript	40s
Unit tests / Elixir / mix coveralls.html	56s
	30m 54s

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