Avoid type mismatch error where a variable is bound with different ref-ness

[nrc]

e.g.,

match x {
      opts::a(ref i) | opts::b(i) => {}
      //~^ ERROR variable `i` is bound with different mode in pattern #2 than in pattern #1
      //~^^ ERROR mismatched types

Where the field of a and b has the same type

cc #30320

[estebank]

Current output, no change:

error[E0409]: variable `i` is bound in inconsistent ways within the same match arm
 --> src/main.rs:8:32
  |
8 |       opts::a(ref i) | opts::b(i) => {}
  |                   -            ^ bound in different ways
  |                   |
  |                   first binding

error[E0308]: mismatched types
 --> src/main.rs:8:32
  |
8 |       opts::a(ref i) | opts::b(i) => {}
  |                                ^ expected &isize, found isize
  |
  = note: expected type `&isize`
             found type `isize`

[estebank]

Current output:

error[E0409]: variable `i` is bound inconsistently across alternatives separated by `|`
 --> src/lib.rs:8:32
  |
8 |       opts::a(ref i) | opts::b(i) => {}
  |                   -            ^ bound in different ways
  |                   |
  |                   first binding

error[E0308]: mismatched types
 --> src/lib.rs:8:32
  |
7 |     match x {
  |           - this expression has type `opts`
8 |       opts::a(ref i) | opts::b(i) => {}
  |               -----            ^ expected `&isize`, found `isize`
  |               |
  |               first introduced with type `&isize` here
  |
  = note: in the same arm, a binding must have the same type in all alternatives
help: consider adding `ref`
  |
8 |       opts::a(ref i) | opts::b(ref i) => {}
  |                                +++

I don't know what else we can do here beyond silencing the E0409.

[estebank]

Triage: no change.

We could silence the E0409 if we detect that we will also emit an E0308, but sadly the former is emitted in resolve, where we don't yet have typeck info, so doing that silencing is going to be difficult. We can do what was originally requested and not emit the E0308, but then we lose the suggestion.