fix(cli): add missing runtime import to test file

go vet reports: cmd/molecule/molecule_test.go:209:11: undefined: runtime

runtime.GOEXE is used in mol() to find the Go binary for building the
test binary. The runtime package was referenced but not imported.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cmd/molecule/molecule_test.go

@@ -8,6 +8,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"runtime"
 	"strings"
 	"testing"
 )