Clear GITPOD_HOST env var before test

This test fails when run (via `go test`) from a gitpod workspace because
gitpod workspaces have the `GITPOD_HOST` env var set, causing the
`NewClient` call to return a `ConfigCatClient` rather than a
`alwaysReturningDefaultValueClient` struct.

Clear the env var before the test runs to avoid this.

Author: Andrew Farries

components/common-go/experiments/types_test.go

@@ -10,6 +10,7 @@ import (
 )
 
 func TestNewClient_WithoutEnvSet(t *testing.T) {
+	t.Setenv("GITPOD_HOST", "")
 	client := NewClient()
 	require.IsType(t, &alwaysReturningDefaultValueClient{}, client)
 }