This PR sets a "magic" environment variable to speed up Goolge stackdriver tests. I'm not 100% sure of the repercussions of this but I dont't think this is the right place to test that we're properly talking to GCP (and I'm not even sure if the test did confirm that). Since we're using slog, we should trust that those APIs work.

Before:

coder@w ~/coder main* ⇣
❯ go test ./cli -count=1 -short -run='TestServer'
ok  	github.com/coder/coder/v2/cli	38.687s

After:

coder@w ~/coder mafredri/test-cli-fix-test-server-logging-stackdriver*
❯ go test ./cli -count=1 -short -run='TestServer'
ok  	github.com/coder/coder/v2/cli	1.604s