Add env to disable finding packages from paths #28945

Job	Run time
syntax	56s
formula audit	6m 36s
tap syntax	5m 5s
cask audit	2m 49s
docker	4m 42s
vendored gems	37s
test default formula (Ubuntu 22.04)	4m 26s
test default formula (Ubuntu 20.04)	6m 12s
update-test (Ubuntu 22.04)	27s
test default formula (macOS 13 x86_64)	2m 30s
tests (online)	8m 57s
update-test (macOS 13)	25s
test default formula (macOS 14 arm64)	1m 17s
tests (generic OS)	5m 57s
tests (Ubuntu 22.04)	6m 14s
tests (Ubuntu 20.04)	7m 42s
tests (macOS 13 x86_64)	8m 18s
tests (macOS 14 arm64)	4m 39s
	1h 17m 49s

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