tests: ruamel.yaml 0.18.13 compatibility

[sebix]

Line wrapping behaves differently since ruamel.yaml version 0.18.13. Additionally it adds spaces at the end of continued lines. https://sourceforge.net/p/ruamel-yaml/code/ci/375c4db4c7c5fad61e149fc0690e50229df23ab3/ So just test now that the file is parseable