[nim] Fix nim code generation in case of an endpoint for which schema defines both query parameters and multipart/form-data

[sandwoodK]

Same parameter name declared multiple time in the same scope. => nim generated code does not compile.

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[sandwoodK]

@hokamoto
this is a fix, because generated nim code does not compile if an endpoint have both query parameters and multipart form data

[wing328]

thanks for the PR

can you please update the samples to fix the CI failure?

[sandwoodK]

Done.
I've amended the previous commit to update samples.

[wing328]

the fix looks good to me

thanks for the contribution.