Fix CI error: "AttributeError: channels"

[nepet]

There are 2 open PRs that produce the same error AttributeError: channels on the following tests:

• libs/gl-testing/tests/test_gl_node.py:127 test_configure_close_to_addr
• libs/gl-testing/tests/test_node.py:143 test_node_invoice_amountless
• libs/gl-testing/tests/test_node.py:186 test_node_listpays_preimage

It seems that the optional channels array returned by listpeers is not reliable anymore. This PR replaces the listpeers calls by listpeerchannels which will return a channels array.