fix(regression): GTK refactor causing updates to be missed

Regression introduced by recent GTK refactor.

The `glib_recv` macros  previously using the passed in expression as the receiver, which was causing a new receiver to be created *every* time an event was received. This caused some peculiar behaviours where some events just never got through if sent too close to each other.

This was most obvious in the `workspaces` module.

Fixes #381

src/image/provider.rs

@@ -145,7 +145,7 @@ impl<'a> ImageProvider<'a> {
         #[cfg(feature = "http")]
         if let ImageLocation::Remote(url) = &self.location {
             let url = url.clone();
-            let (tx, mut rx) = mpsc::channel(64);
+            let (tx, rx) = mpsc::channel(64);
 
             spawn(async move {
                 let bytes = Self::get_bytes_from_http(url).await;