Update unoptimized_previous_button.dart / Fixed canGoToPreviousPagePr… #4349

Job	Run time
build (master, examples/counter)	1m 32s
build (master, examples/marvel)	1m 29s
build (master, examples/pub)	1m 27s
build (master, examples/random_number)	1m 42s
build (master, examples/stackoverflow)	2m 0s
build (master, examples/todos)	2m 12s
build (master, packages/riverpod)	3m 11s
build (master, packages/riverpod/example)	1m 33s
build (master, packages/flutter_riverpod)	1m 49s
build (master, packages/flutter_riverpod/example)	2m 0s
build (master, packages/hooks_riverpod)	1m 30s
build (master, packages/hooks_riverpod/example)	1m 25s
build (master, packages/riverpod_annotation)	1m 4s
build (master, packages/riverpod_generator)	1m 55s
build (master, packages/riverpod_generator/integration/build_yaml)	1m 56s
build (master, website)	1m 57s
	28m 42s

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