Is this what you had in mind?

Closes #11493

fuzz: Fixes broken Cargo.toml for fuzz tests

Fixes broken Cargo.toml for fuzz tests and adds building of fuzz tests to the CI.

…t-lang#14010)

Proposing to replace

```rust
let mut x = PathBuf::from("/foo");
x.push("/bar");
```

by

```rust
let mut x = PathBuf::from("/foo");
x.push("bar");
```

changes the content of `x` (`/bar` ⇒ `/foo/bar`). This is not equivalent
and should not be `MachineApplicable`, even if the original code is
suspicious.

changelog: none