Override vargo target dir #6385

Job	Run time
smoke-test-and-release-linux	6m 24s
smoke-test-and-release-windows	7m 50s
smoke-test-and-release-macos-x86	10m 56s
fmt	1m 16s
test-and-release-macos	10m 43s
test-and-release-macos (record-history)	2m 58s
test-and-release-macos (no-std)	3m 23s
test-and-release-macos (no-alloc)	2m 49s
test-and-release-macos (singular)	3m 47s
test-and-release-macos (cvc5)	2m 25s
release	25s
	52m 56s

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