fix(rest): properly parse body parameters when mixed with oneOf

[yassine-bhn]

Fixes an issue where endpoints that declare properties at the top level alongside a oneOf field (like Create a check run) were missing those top-level properties. It also fixes oneOf elements without 'type: object'.
#4365

[github-actions]

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[github-actions]

👋 Hey there spelunker. It looks like you've modified some files that we can't accept as contributions:

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