Fix profile goldens, pin source_span dependency #2549

Job	Run time
flutter_packages (packages/rx_bloc_list)	3m 10s
packages (packages/rx_bloc)	2m 8s
flutter_packages (packages/flutter_rx_bloc)	3m 15s
examples (examples/booking_app)	2m 39s
packages (packages/rx_bloc_test)	2m 30s
cli_packages (packages/rx_bloc_cli)	2m 26s
examples (examples/counter)	1m 53s
packages (packages/rx_bloc_generator)	3m 34s
examples (examples/division)	1m 40s
examples (examples/favorites_advanced/rx_bloc_favorites_advanced)	2m 6s
examples (examples/todoapp)	3m 4s
build	0s
	28m 25s

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