Rollup merge of #152698 - Zalathar:zforce, r=jieyouxu

Suppress unstable-trait notes under `-Zforce-unstable-if-unmarked`

- Fixes rust-lang/rust#152692.
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rust-lang/rust#151036 adds extra diagnostic text (“the nightly-only, unstable trait”) to note when a not-implemented trait is unstable.

However, that extra text is usually unhelpful when building a crate graph with `-Zforce-unstable-if-unmarked` (such as the compiler or stdlib), because *any* trait not explicitly marked stable will be treated as unstable.

(For typical compiler contributors using the stage0 compiler, this fix won't take effect until the next bootstrap beta bump.)

Author: Zalathar