Build media and live-kit in test-mode on non-MacOS (#6859)

Build media and live-kit in test-mode on non-MacOS (Related to
https://github.com/zed-industries/zed/issues/5391
https://github.com/zed-industries/zed/issues/5395
https://github.com/zed-industries/zed/issues/5394)

This makes it possible to build the media and live-kit crates on
non-MacOS

Release Notes:

- N/A

crates/live_kit_client/src/test.rs

@@ -5,6 +5,7 @@ use collections::{BTreeMap, HashMap, HashSet};
 use futures::Stream;
 use gpui::BackgroundExecutor;
 use live_kit_server::{proto, token};
+#[cfg(target_os = "macos")]
 use media::core_video::CVImageBuffer;
 use parking_lot::Mutex;
 use postage::watch;
@@ -845,6 +846,7 @@ impl Frame {
         self.height
     }
 
+    #[cfg(target_os = "macos")]
     pub fn image(&self) -> CVImageBuffer {
         unimplemented!("you can't call this in test mode")
     }