version-gate the trailing semicolon change of return statements inside a match arm

[scampi]

Close #3229

[scampi]

The error comes from futures-rs which doesn't compile:

error[E0432]: unresolved import `std::marker::Pinned`
 --> futures-test/src/future/assert_unmoved.rs:4:5
  |
4 | use std::marker::Pinned;
  |     ^^^^^^^^^^^^^^^^^^^ no `Pinned` in `marker`

[topecongiro]

LGTM, thanks!