fixes rust-lang#125189

… r=Mark-Simulacrum

tidy: stop special-casing tests/ui entry limit

It is genuinely more annoying to have this error, now that this value is below the general `ENTRY_LIMIT` cap, when one is trying to clean out tests from tests/ui! This code has served its purpose well, let it rest now rather than force it to continue haunting us.

…=Mark-Simulacrum

Create a triagebot ping group for Rust for Linux

Corresponding rustc-dev-guide PR [here](rust-lang/rustc-dev-guide#1984). Discussed on [Zulip](https://rust-lang.zulipchat.com/#narrow/stream/242791-t-infra/topic/Testing.20Rust.20for.20Linux.20in.20our.20CI).

A small diagnostic improvement for dropping_copy_types

For a value `m`  which implements `Copy` trait, `drop(m);` does nothing.
We now suggest user to ignore it by a abstract and general note: `let _ = ...`.
I think we can give a clearer note here: `let _ = m;`

fixes rust-lang#125189

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Stop SRoA'ing `DynMetadata` in MIR

Fixes rust-lang#125506

cleanup dependence of `ExtCtxt` in transcribe when macro expansion

part of rust-lang#125356
We can remove `transcribe`’s dependence on `ExtCtxt` to facilitate subsequent work (such as moving macro expansion into the incremental compilation system)

r? ```@petrochenkov```
Thanks for the reviewing!

…ific, r=Mark-Simulacrum

Also mention my-self for other check-cfg docs changes

This PR adds a mention for my-self for the recently added `src/doc/rustc/src/check-cfg` directory.

*I had to add a second mention just for the directory since [`Path::starts_with`](https://doc.rust-lang.org/std/path/struct.Path.html#method.starts_with) as used by [triagebot](https://github.com/rust-lang/triagebot/blob/48f29f351cae774caa90f555fbbc6d0df7dce80e/src/handlers/mentions.rs#L69), matches on path components and so can never return true for a file and directory at the same time.*

…=workingjubilee

Simplify the `unchecked_sh[lr]` ub-checks a bit

It can use the constant in the check, rather than passing it as a parameter.