bug: Data class not generated if schema contains allOf

[andlbrei]

This is not a PR for a fix, this PR contains my findings while investigating the issue, as requested by @wing328 in #19755

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[wing328]

i've filed #19964 to workaround issues. tested with the spec you provided and the result seems good

can you please also give it a try?

[andlbrei]

Thanks @wing328 !
This seems to be working, indeed.