doc: replace pub run with dart run (#141) #1139

Job	Run time
Test Flutter beta on ubuntu-latest	3m 23s
Test Flutter stable on windows-latest	8m 36s
Test Flutter beta on windows-latest	6m 10s
Test Flutter beta on macos-latest	6m 25s
Test Flutter stable on macos-latest	3m 51s
Test Flutter stable on ubuntu-latest	2m 55s
	31m 20s

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