Add test for spawning a local task from a different prio

This ensures that there is no method on the spawning
task's local spawner for spawning the local task
with the other priority.

rtic-macros/ui/spawn-local-different-exec.rs

@@ -0,0 +1,25 @@
+#![no_main]
+
+#[rtic_macros::mock_app(device = mock, dispatchers = [EXTI0])]
+mod app {
+    use super::*;
+
+    #[shared]
+    struct Shared {}
+
+    #[local]
+    struct Local {}
+
+    #[init]
+    fn init(_cx: init::Context) -> (Shared, Local) {
+        (Shared {}, Local {})
+    }
+
+    #[task(priority = 1, is_local_task = true)]
+    async fn foo(_cx: foo::Context) {}
+
+    #[task(priority = 2)]
+    async fn bar(cx: bar::Context) {
+        cx.local_spawner.foo().ok();
+    }
+}