tests: Clarify transport config tests optimisation & correct value

The ini inventory parser doesn't support comments after a value, so the value
parsed was "python3000  # Not expected to exist".

tests/ansible/hosts/transport_config.hosts

@@ -20,11 +20,12 @@ tc_remote_user
 tc_transport
 
 [transport_config_undiscover:vars]
-# If python interpreter path is unset, Ansible tries to connect & discover it.
+# If ansible_*_interpreter isn't set Ansible tries to connect & discover it.
-# That causes approx 10 seconds timeout per task - there's no host to connect to.
+# If that target doesn't exist we must wait $timeout seconds for each attempt.
+# Setting a known (invalid) interpreter skips discovery & the many timeouts.
 # This optimisation should not be relied in any test.
 # Note: tc-python-path-* are intentionally not included.
-ansible_python_interpreter = python3000  # Not expected to exist
+ansible_python_interpreter = python3000
 
 [tc_transport]
 tc-transport-unset