error[E0308]: mismatched types
  --> src/main.rs:21:18
   |
21 |     let result = generic_fn(foo, &a).await;
   |                  ^^^^^^^^^^^^^^^^^^^ one type is more general than the other
   |
   = note: expected trait `for<'a, 'b, 'c> Fn(&'a i32, &'b i32, &'c i32)`
              found trait `for<'a, 'b> Fn(&'a i32, &'b i32, &'b i32)`
note: the lifetime requirement is introduced here
  --> src/main.rs:10:8
   |
10 |     F: Fn(&i32, &i32, &i32) -> Fut,
   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0308]: mismatched types
  --> src/main.rs:21:18
   |
21 |     let result = generic_fn(foo, &a).await;
   |                  ^^^^^^^^^^^^^^^^^^^ one type is more general than the other
   |
   = note: expected opaque type `impl for<'a, 'b> Future<Output = i32>`
              found opaque type `impl Future<Output = i32>`
   = help: consider `await`ing on both `Future`s
   = note: distinct uses of `impl Trait` result in different opaque types
note: the lifetime requirement is introduced here
  --> src/main.rs:10:32
   |
10 |     F: Fn(&i32, &i32, &i32) -> Fut,
   |                                ^^^

error[E0308]: mismatched types
  --> src/main.rs:21:18
   |
21 |     let result = generic_fn(foo, &a).await;
   |                  ^^^^^^^^^^^^^^^^^^^ one type is more general than the other
   |
   = note: expected trait `for<'a, 'b, 'c> FnOnce(&'a i32, &'b i32, &'c i32)`
              found trait `for<'a, 'b> FnOnce(&'a i32, &'b i32, &'b i32)`
note: the lifetime requirement is introduced here
  --> src/main.rs:10:32
   |
10 |     F: Fn(&i32, &i32, &i32) -> Fut,
   |                                ^^^

For more information about this error, try `rustc --explain E0308`.

I ended up resolving this by avoiding using the references inside the generic function and instead pass them by value. It leads to a copy, but it works fine for my use case. I could have also probably used an Arc, but I'm fine with copying.

Here's a working example:
https://gist.github.com/rcythr/16a70560c4292eae4a45979d8163515a