Integer mismatch incorrectly suggests `T::from()` as LHS of assignment

[Reconcyl]

I tried the following code (playground link):

fn main() {
    let mut a: u8 = 0;
    let b: u32 = 0;
    a = b;
}

I expected the compiler to recommend using b.try_into().unwrap() to convert it into a u8. This seems to have been the case in version 1.37.0. Instead, it produces the following error message on stable, beta, and nightly:

error[E0308]: mismatched types
 --> src/main.rs:4:9
  |
4 |     a = b;
  |         ^ expected `u8`, found `u32`
  |
help: you can convert `a` from `u8` to `u32`, matching the type of `b`
  |
4 |     u32::from(a) = b;
  |     ^^^^^^^^^^^^

The suggestion is incorrect, as the return value of a function call is not assignable.

[camelid]

Fixed in #81325.