Backport #35610 by @surya-purohit
Updates the swagger documentation for the `diffpatch` API endpoint.
The request body is corrected from the outdated `UpdateFileOptions` to
the current `ApplyDiffPatchOptions` to match the code implementation.
Closes [issue#35602](https://github.com/go-gitea/gitea/issues/35602)
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Co-authored-by: Surya Purohit <suryaprakash.sharma@sourcefuse.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
