Fix build for ARM

[realtica]

OS: Debian GNU/Linux 10 (buster) aarch64

cargo 1.56.0 (4ed5d137b 2021-10-04)

error[E0308]: mismatched types
  --> packages/hurl/src/runner/xpath.rs:97:45
   |
97 |             let x = unsafe { CStr::from_ptr(c_s2) };
   |                                             ^^^^ expected `u8`, found `i8`
   |
   = note: expected raw pointer `*const u8`
              found raw pointer `*const i8`

For more information about this error, try `rustc --explain E0308`.
error: could not compile `hurl` due to previous error
warning: build failed, waiting for other jobs to finish...
error: build failed

Please I do know what happened.

[fabricereix]

Thanks for reporting the issue.
We haven't built/tested Hurl on ARM architecture yet. We are going to look into it

[fabricereix]

We have reproduced the error.
We are going to add a ARM-specific CI build (#335)