Fixing spawn_test for go 1.21

[pfgray]

In go 1.21, go env changed the way it printed values

go version < 1.21:

GOPATH="/vaulted"
...

go >= 1.21:

GOPATH='/vaulted'
...

Which causes spawn_test.go to fail, since it's looking for exactly GOPATH="/vaulted" in go env's output.

This commit updates the test to look for single quotes or double quotes, making it compatible with all versions of go.