[ci] Enabled metal tests on macOS

Author: syl20bnr

xtask/src/commands/test.rs

@@ -51,6 +51,11 @@ pub(crate) fn handle_command(
                 ]);
             };
 
+            let mut features = args.features.unwrap_or_default();
+            #[cfg(target_os = "macos")]
+            features.push("metal".to_string());
+            args.features = Some(features);
+
             // test workspace
             base_commands::test::handle_command(args.try_into().unwrap())?;