Auto merge of #9714 - PTNobel:fix-force-warn, r=ehuss

Changes rustc argument from `--force-warns` to `--force-warn`

The rustc argument was renamed in rust-lang/rust#87346 breaking `cargo fix` on the nightly toolchain.

I encountered this while attempting to test Edition 2021 migrations.

I ran `RUSTC=/path/to/nightly/rustc cargo test` and encountered a few failing tests, but none of them seemed at all related to the 1 line I changed, so if they crop up in CI as well, would love some help on identifying what's causing that.

Closes rust-lang/rust#87360