Suppress "unbound variable" error. (#14424)
Suppress "unbound variable" error. (#14424)

Without this change, you'd see this error:

```
./run-tests.sh: line 49: LAMBDA_TESTS_ENABLED: unbound variable
./run-tests.sh: line 49: LAMBDA_TESTS_ENABLED: unbound variable
```
hashicorp/consul,hashicorp/consul,hashicorp/consul,hashicorp/consul