pallet-core-fellowship: import an unimported member on approve (#2883)

To align with the documentation of the approve call, we import an
unimported member on approval.

No changes have been made to the benchmarks as they already cover the
worst-case scenario.

substrate/frame/core-fellowship/src/tests.rs

@@ -378,3 +378,11 @@ fn active_changing_get_salary_works() {
 		}
 	});
 }
+
+#[test]
+fn approve_imports_not_tracked_member() {
+	new_test_ext().execute_with(|| {
+		set_rank(10, 5);
+		assert_ok!(CoreFellowship::approve(signed(5), 10, 5));
+	});
+}