Tests

Refactor env::which #147

Job	Run time
Unix tests (ubuntu-latest, debug) / Build binaries	4m 51s
Unix tests (macos-latest, release) / Build binaries	7m 57s
Unix tests (ubuntu-latest, release) / Build binaries	51s
Unix tests (macos-latest, debug) / Build binaries	10m 34s
Windows tests (windows-2019, release) / Build binaries	7m 30s
Unix tests (ubuntu-latest, release) / Test libmamba	39s
Unix tests (ubuntu-latest, release) / Test libmamba Python bindings	1m 0s
Unix tests (ubuntu-latest, release) / Test integration micromamba	15m 16s
Unix tests (ubuntu-latest, debug) / Test libmamba Python bindings	1m 2s
Unix tests (ubuntu-latest, debug) / Test integration micromamba	17m 18s
Unix tests (ubuntu-latest, debug) / Test libmamba	48s
Windows tests (windows-2019, release) / Test integration micromamba	44m 24s
Windows tests (windows-2019, release) / Test libmamba	2m 56s
Windows tests (windows-2019, release) / Test libmamba Python bindings	2m 26s
Unix tests (macos-latest, release) / Test integration micromamba	49m 32s
Unix tests (macos-latest, release) / Test libmamba Python bindings	2m 5s
Unix tests (macos-latest, release) / Test libmamba	1m 58s
Unix tests (macos-latest, debug) / Test libmamba	2m 7s
Unix tests (macos-latest, debug) / Test libmamba Python bindings	3m 28s
Unix tests (macos-latest, debug) / Test integration micromamba	54m 10s
	3h 50m 52s

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