watch: fix interaction with multiple env files #662

Job	Run time
Build slim tarball	1m 27s
aarch64-linux: with shared libraries	49m 36s
x86_64-linux: with shared libraries	57m 18s
aarch64-darwin: with shared libraries	48m 59s
x86_64-darwin: with shared libraries	41m 53s
	3h 19m 13s

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