Rollup merge of #148451 - Enselic:tidy-fix, r=clubby789

tidy: Fix false positives with absolute repo paths in `pal.rs` `check()`

Fixes this bug:

#### Step-by-step
1. `git clone https://github.com/rust-lang/rust.git rust-improve-tests`
2. `cd rust-improve-tests`
3. `./x test tidy`

#### Expected
No tidy errors found

#### Actual
```
thread 'pal (library)' (837175) panicked at src/tools/tidy/src/pal.rs:100:5:
assertion failed: saw_target_arch
```
#### Explanation

Since the git checkout dir contains the word ["tests"](https://github.com/rust-lang/rust/blob/bf0ce4bc6816e3b9aaa52dc5fd47b8b5b2e0cd50/src/tools/tidy/src/pal.rs#L96), the `pal.rs` `check()` used to erroneously ignore all paths.