Fix relationship macro for multiple named members fields (#18530)

# Objective

Fixes #18466 

## Solution

Updated the macro generation pattern to place the comma in the correct
place in the pattern.

## Testing

- Tried named and unnamed fields in combination, and used rust expand
macro tooling to see the generated code and verify its correctness (see
screenshots in example below)

---

## Showcase

Screenshot showing expanded macro with multiple named fields

![image](https://github.com/user-attachments/assets/7ecd324c-10ba-4b23-9b53-b94da03567d3)

Screenshot showing expanded macro with single unnamed field

![image](https://github.com/user-attachments/assets/be72f061-5f07-4d19-b5f6-7ff6c35ec679)

## Migration Guide

n/a

crates/bevy_ecs/macros/src/component.rs

@@ -746,7 +746,7 @@ fn derive_relationship(
             #[inline]
             fn from(entity: #bevy_ecs_path::entity::Entity) -> Self {
                 Self {
-                    #(#members: core::default::Default::default(),),*
+                    #(#members: core::default::Default::default(),)*
                     #relationship_member: entity
                 }
             }
@@ -809,7 +809,7 @@ fn derive_relationship_target(
             #[inline]
             fn from_collection_risky(collection: Self::Collection) -> Self {
                 Self {
-                    #(#members: core::default::Default::default(),),*
+                    #(#members: core::default::Default::default(),)*
                     #relationship_member: collection
                 }
             }

crates/bevy_ecs/src/relationship/mod.rs

@@ -385,4 +385,41 @@ mod tests {
         assert!(!world.entity(b).contains::<Rel>());
         assert!(!world.entity(b).contains::<RelTarget>());
     }
+
+    #[test]
+    fn relationship_with_multiple_non_target_fields_compiles() {
+        #[derive(Component)]
+        #[relationship(relationship_target=Target)]
+        #[expect(dead_code, reason = "test struct")]
+        struct Source {
+            #[relationship]
+            target: Entity,
+            foo: u8,
+            bar: u8,
+        }
+
+        #[derive(Component)]
+        #[relationship_target(relationship=Source)]
+        struct Target(Vec<Entity>);
+
+        // No assert necessary, looking to make sure compilation works with the macros
+    }
+    #[test]
+    fn relationship_target_with_multiple_non_target_fields_compiles() {
+        #[derive(Component)]
+        #[relationship(relationship_target=Target)]
+        struct Source(Entity);
+
+        #[derive(Component)]
+        #[relationship_target(relationship=Source)]
+        #[expect(dead_code, reason = "test struct")]
+        struct Target {
+            #[relationship]
+            target: Vec<Entity>,
+            foo: u8,
+            bar: u8,
+        }
+
+        // No assert necessary, looking to make sure compilation works with the macros
+    }
 }