Make new auto_explain test safe for log_error_verbosity = verbose.
Allow for the possible presence of a SQLSTATE code in the expected
warning message, similarly to
b998196bb and
19408aae7 (although
here I see no need to allow more than one specific SQLSTATE).
Per gripe from Andrew Dunstan.
Discussion: https://postgr.es/m/
c550ac53-5db5-3958-1798-
50bae3d9af71@dunslane.net