[Minor] Fix error messages for shrink and try_shrink (#20422)

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- Closes #.

## Rationale for this change

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In the following code, when we fetch `prev` again to construct the error
message, the value we get may be different from the value that failed
`checked_sub` in the first place which would get us out of the
fetch_update CAS loop. Instead we should use the prev value that
`fetch_update` returned in the error message.

```rust
pub fn try_shrink(&self, capacity: usize) -> Result<usize> {
    let prev = self
        .size
        .fetch_update(
            atomic::Ordering::Relaxed,
            atomic::Ordering::Relaxed,
            |prev| prev.checked_sub(capacity),
        )
        .map_err(|_| {
            let prev = self.size.load(atomic::Ordering::Relaxed);
            internal_datafusion_err!(
                "Cannot free the capacity {capacity} out of allocated size {prev}"
            )
        })?;

    self.registration.pool.shrink(self, capacity);
    Ok(prev - capacity)
}
```

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Yes, with existing tests.

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No

Author: hareshkh

datafusion/execution/src/memory_pool/mod.rs

@@ -391,7 +391,9 @@ impl MemoryReservation {
                 atomic::Ordering::Relaxed,
                 |prev| prev.checked_sub(capacity),
             )
-            .expect("capacity exceeds reservation size");
+            .unwrap_or_else(|prev| {
+                panic!("Cannot free the capacity {capacity} out of allocated size {prev}")
+            });
         self.registration.pool.shrink(self, capacity);
     }
 
@@ -407,8 +409,7 @@ impl MemoryReservation {
                 atomic::Ordering::Relaxed,
                 |prev| prev.checked_sub(capacity),
             )
-            .map_err(|_| {
-                let prev = self.size.load(atomic::Ordering::Relaxed);
+            .map_err(|prev| {
                 internal_datafusion_err!(
                     "Cannot free the capacity {capacity} out of allocated size {prev}"
                 )