Strawberry Shake generates invalid C# for mutations with multiple uploads

[karlanke]

Product

Strawberry Shake

Version

14.3.0

Link to minimal reproduction

N/A

Steps to reproduce

Point StrawberryShake at a schema like:
`input InsuranceUpdate {
...
"The back of the insurance card"
insurance_card_back: Upload

"The front of the insurance card"
insurance_card_front: Upload
...
}`

What is expected?

Valid C# is generated.

What is actually happening?

error CS0128: A local variable or function named 'u' is already defined in this scope

Relevant log output

Additional context

PR incoming.