[RUST] Upgrade reqwest-middleware

[RemiKalbe]

Simply bump reqwest-middleware to its latest version: 0.2.0

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@frol @farcaller @richardwhiuk @paladinzh @jacob-pro

[wing328]

also tested locally and the result is good

   Compiling petstore-reqwest-async-middleware v1.0.0 (/Users/williamcheng/Code/openapi-generator7/samples/client/petstore/rust/reqwest/petstore-async-middleware)
warning: unused variable: `file`
   --> reqwest/petstore-async-middleware/src/apis/pet_api.rs:507:9
    |
507 |     let file = params.file;
    |         ^^^^ help: if this is intentional, prefix it with an underscore: `_file`
    |
    = note: `#[warn(unused_variables)]` on by default

warning: `petstore-reqwest-async-middleware` (lib) generated 1 warning
    Finished dev [unoptimized + debuginfo] target(s) in 7m 10s