Rollup merge of #72527 - RalfJung:miri-clippy-test-args, r=Mark-Simulacrum

bootstrap: propagate test-args to miri and clippy test suites

For Miri I verified this works. For clippy, unfortunately it doesn't seem to work as a stage 0 tool:
```
./x.py --stage 0 test src/tools/clippy --test-args init
```
gives
```
   Compiling clippy-mini-macro-test v0.2.0 (/home/r/src/rust/rustc.3/src/tools/clippy/mini-macro)
error[E0658]: procedural macros cannot be expanded to expressions
  --> src/tools/clippy/mini-macro/src/lib.rs:11:5
   |
11 | /     quote!(
12 | |         #[allow(unused)]
13 | |         fn needless_take_by_value(s: String) {
14 | |             println!("{}", s.len());
...  |
24 | |         }
25 | |     )
   | |_____^
   |
   = note: see issue #54727 <https://github.com/rust-lang/rust/issues/54727> for more information
   = help: add `#![feature(proc_macro_hygiene)]` to the crate attributes to enable

   Compiling proc-macro2 v1.0.3
   Compiling syn v1.0.11
error: aborting due to previous error

For more information about this error, try `rustc --explain E0658`.
error: could not compile `clippy-mini-macro-test`.
```
But propagating `--test-args` to the test suite seems to make sense regardless.
Cc @rust-lang/clippy

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