Rollup merge of #67701 - petrochenkov:tidybless, r=Mark-Simulacrum

Rollup merge of #67701 - petrochenkov:tidybless, r=Mark-Simulacrum

tidy: Enforce formatting rather than just check it if `--bless` is specified

Ensuring the "tidy"-ness currently requires running `rustfmt` twice:
```sh
./x.py fmt && ./x.py test tidy
```
, once to actually format code and the second time as a part of tidy to check that the code is formatted.

Running `rustfmt` is slow, so we don't want to run it twice.

With this PR tidy enforces the formatting rather than just checks it if `--bless` was passed to it:
```sh
./x.py test tidy --bless
```

r? @Mark-Simulacrum