Ignore manual_c_str_literals warning.

Due to https://github.com/rust-lang/rust-clippy/issues/13531, this
incorrectly applies here on nightly builds of clippy -- it should not,
since this project is on edition 2015 by default.

src/backend/mod.rs

@@ -2645,6 +2645,8 @@ impl ContextOps for AudioUnitContext {
     }
 
     fn backend_id(&mut self) -> &'static CStr {
+        // https://github.com/rust-lang/rust-clippy/issues/13531
+        #[allow(clippy::manual_c_str_literals)]
         unsafe { CStr::from_ptr(b"audiounit-rust\0".as_ptr() as *const _) }
     }
     #[cfg(target_os = "ios")]