refactor(kernel): ignore the clippy::extra_unused_type_parameters lint in unboost_priority

`r3_kernel::state::unboost_priority` triggers this lint when
`cfg(not(feature = "priority_boost"))`.

Author: yvt

src/r3_kernel/src/state.rs

@@ -61,6 +61,7 @@ pub(super) fn unboost_priority<Traits: KernelTraits>() -> Result<(), BoostPriori
 
 /// Implements `Kernel::unboost_priority`.
 #[cfg(not(feature = "priority_boost"))]
+#[expect(clippy::extra_unused_type_parameters)]
 pub(super) fn unboost_priority<Traits: KernelTraits>() -> Result<(), BoostPriorityError> {
     // Priority Boost is disabled statically, so this function will always
     // return `BadContext`