Move s3cmd installation to before_install, fix extra slash in destina… #49

Job	Run time
MacOS	5m 46s
Ubuntu	30m 23s
Read .env file and expose it as output	5s
Windows (2019) / windows-2019	34m 55s
Windows (2022) / windows-2022	36m 28s
	1h 47m 37s

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