pipewire: properties!{} macro uses freed memory

Thanks clippy:

warning: getting the inner pointer of a temporary `CString`
   --> pipewire/src/properties.rs:58:57
    |
58  |                       std::ffi::CString::new($k).unwrap().as_ptr(),
    |                       ----------------------------------- ^^^^^^ this pointer will be invalid
    |                       |
    |                       this `CString` is deallocated at the end of the statement, bind it to a variable to extend its lifetime
...
219 |           let props = properties! {
    |  _____________________-
220 | |             "K0" => "V0"
221 | |         };
    | |_________- in this macro invocation
    |
    = note: pointers do not have a lifetime; when calling `as_ptr` the `CString` will be deallocated at the end of the statement because nothing is referencing it as far as the type system is concerned
    = help: for more information, see https://doc.rust-lang.org/reference/destructors.html
    = note: `#[warn(temporary_cstring_as_ptr)]` on by default
    = note: this warning originates in the macro `properties` (in Nightly builds, run with -Z macro-backtrace for more info)

This means that we're freeing the CStrings before calling the functions, the pointers point to freed memory.

The macro code is here: https://gitlab.freedesktop.org/pipewire/pipewire-rs/-/blob/main/pipewire/src/properties.rs#L53

I can't figure out how to solve this. Because we're using a variadic macro, it doesn't seem possible to bind each argument to a variable before the function call.

Rust RFC 3086 could help because we could stick all args in a Vector and then index it with the current repition number, but the implementation is still unstable.