fix unloading stateful check (vercel/turborepo#8749)

### Description

We need to move up the check so it prevents unloading tasks with state.

### Testing Instructions

<!--
  Give a quick description of steps to test your changes.
-->

crates/turbo-tasks-memory/src/task.rs

@@ -1621,22 +1621,22 @@ impl Task {
  }
  state.gc.generation = None;
 
- if active {
- let mut cells_to_drop = Vec::new();
-
- match &mut state.state_type {
- TaskStateType::Done { stateful, edges: _ } => {
- if *stateful {
- return GcResult::NotPossible;
- }
- }
- TaskStateType::Dirty { .. } => {}
- _ => {
- // GC can't run in this state. We will reschedule it when the execution
- // completes.
+ match &mut state.state_type {
+ TaskStateType::Done { stateful, edges: _ } => {
+ if *stateful {
  return GcResult::NotPossible;
  }
  }
+ TaskStateType::Dirty { .. } => {}
+ _ => {
+ // GC can't run in this state. We will reschedule it when the execution
+ // completes.
+ return GcResult::NotPossible;
+ }
+ }
+
+ if active {
+ let mut cells_to_drop = Vec::new();
 
  // shrinking memory and dropping cells
  state.aggregation_node.shrink_to_fit();