build(deps): bump dart-lang/setup-dart from 1.3.0 to 1.6.0 #89

Job	Run time
cancel-previous-workflow	4s
android \| ubuntu-latest \| stable	1m 6s
android \| ubuntu-latest \| beta	1m 0s
linux \| ubuntu-latest \| stable	1m 27s
linux \| ubuntu-latest \| beta	1m 17s
ios \| macos-latest \| stable	1m 53s
macos \| macos-latest \| stable	1m 33s
windows \| windows-latest \| stable	2m 13s
windows \| windows-latest \| beta	2m 9s
analyze / analyze	1m 48s
analyze / cancel-previous-workflow	3s
analyze / package-analysis	44s
	15m 17s

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