servo: Merge #16150 - Allow using servo as dependency, by fixing Cargo.toml of servo-test-t… (from kdy1997:master); r=jdm

- [ ] `./mach build -d` does not report any errors
I had hard time trying to compile rust-mozjs on my ubuntu machine, and I gave up. As this pr does not touch any source code, I expect it to be work.

- [x] `./mach test-tidy` does not report any errors

```sh
Checking the config file...
Checking directories for correct file extensions...

tidy reported no errors.
```

- [x] These changes fix #16149 (github issue number if applicable).

- [x] These changes do not require tests because it's trivial.

Source-Repo: https://github.com/servo/servo
Source-Revision: 9eb6bb78b0dc7ab0f79f7dc992764225c8dcac1d

servo/python/tidy/servo_tidy_tests/Cargo.toml

@@ -6,3 +6,6 @@ publish = false
 
 [dependencies]
 test-package = { version = "*" }
+
+[lib]
+path = "lib.rs"