watch: fix interaction with multiple env files #709

Job	Run time
Build slim tarball	1m 34s
aarch64-linux: with shared libraries	28m 49s
x86_64-linux: with shared libraries	32m 57s
aarch64-darwin: with shared libraries	27m 7s
x86_64-darwin: with shared libraries	2h 2m 15s
	3h 32m 42s

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