nuageninit: modify the test to show the issue fixed inc316ec259011

Ensure the script used is invalid when parsed by libyaml which
highlight the issue revealed in PR295062

while at here validate the

nuageninit: modify the test to show the issue fixed inc316ec259011

Ensure the script used is invalid when parsed by libyaml which
highlight the issue revealed in PR295062

while at here validate the mode of the file is properly changed

PR: 295062
MFC After: 1 day

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