fix: make lease functions less chatty

Without this change, the consule would be filled with
"failed to release lease: lease not found" even if flyctl couldn't acquire
one lease.

```
Updating existing machines in '...' with bluegreen strategy
WARN failed to acquire lease: failed to get lease on VM e7843075ad2408: request returned non-2xx status: 408:

WARN failed to release lease for machine 178122df9672d8: lease not found

WARN failed to release lease: lease not found

WARN failed to release lease for machine 7811772a5d7698: lease not found

WARN failed to release lease: lease not found

WARN failed to release lease for machine e286076f933508: lease not found

WARN failed to release lease: lease not found
...
```

internal/machine/leasable_machine.go

@@ -516,6 +516,7 @@ func (lm *leasableMachine) refreshLeaseUntilCanceled(ctx context.Context, durati
 	}
 }
 
+// ReleaseLease releases the lease on this machine.
 func (lm *leasableMachine) ReleaseLease(ctx context.Context) error {
 	lm.mu.Lock()
 	defer lm.mu.Unlock()
@@ -536,13 +537,7 @@ func (lm *leasableMachine) ReleaseLease(ctx context.Context) error {
 		defer cancel()
 	}
 
-	err := lm.flapsClient.ReleaseLease(ctx, lm.machine.ID, nonce)
-	contextTimedOutOrCanceled := errors.Is(err, context.DeadlineExceeded) || errors.Is(err, context.Canceled)
-	if err != nil && (!contextWasAlreadyCanceled || !contextTimedOutOrCanceled) {
-		terminal.Warnf("failed to release lease for machine %s: %v\n", lm.machine.ID, err)
-		return err
-	}
-	return nil
+	return lm.flapsClient.ReleaseLease(ctx, lm.machine.ID, nonce)
 }
 
 func (lm *leasableMachine) resetLease() {

internal/machine/machine_set.go

@@ -15,6 +15,7 @@ import (
 	"github.com/superfly/flyctl/internal/tracing"
 	"github.com/superfly/flyctl/iostreams"
 	"github.com/superfly/flyctl/terminal"
+	"golang.org/x/sync/errgroup"
 )
 
 type MachineSet interface {
@@ -49,36 +50,27 @@ func (ms *machineSet) GetMachines() []LeasableMachine {
 	return ms.machines
 }
 
+// AcquireLeases acquires leases on all machines in the set for the given duration.
 func (ms *machineSet) AcquireLeases(ctx context.Context, duration time.Duration) error {
 	if len(ms.machines) == 0 {
 		return nil
 	}
 
-	results := make(chan error, len(ms.machines))
-	var wg sync.WaitGroup
+	// Don't override ctx. Even leaseCtx is cancelled, we still want to release the leases.
+	eg, leaseCtx := errgroup.WithContext(ctx)
 	for _, m := range ms.machines {
-		wg.Add(1)
-		go func(m LeasableMachine) {
-			defer wg.Done()
-			results <- m.AcquireLease(ctx, duration)
-		}(m)
+		eg.Go(func() error {
+			return m.AcquireLease(leaseCtx, duration)
+		})
 	}
-	go func() {
-		wg.Wait()
-		close(results)
-	}()
-	hadError := false
-	for err := range results {
-		if err != nil {
-			hadError = true
-			terminal.Warnf("failed to acquire lease: %v\n", err)
-		}
-	}
-	if hadError {
+
+	waitErr := eg.Wait()
+	if waitErr != nil {
+		terminal.Warnf("failed to acquire lease: %v\n", waitErr)
 		if err := ms.ReleaseLeases(ctx); err != nil {
 			terminal.Warnf("error releasing machine leases: %v\n", err)
 		}
-		return fmt.Errorf("error acquiring leases on all machines")
+		return waitErr
 	}
 	return nil
 }
@@ -100,6 +92,7 @@ func (ms *machineSet) RemoveMachines(ctx context.Context, machines []LeasableMac
 	return subset.ReleaseLeases(ctx)
 }
 
+// ReleaseLeases releases leases on all machines in this set.
 func (ms *machineSet) ReleaseLeases(ctx context.Context) error {
 	if len(ms.machines) == 0 {
 		return nil
@@ -130,10 +123,15 @@ func (ms *machineSet) ReleaseLeases(ctx context.Context) error {
 	}()
 	hadError := false
 	for err := range results {
-		contextTimedOutOrCanceled := errors.Is(err, context.DeadlineExceeded) || errors.Is(err, context.Canceled)
-		if err != nil && (!contextWasAlreadyCanceled || !contextTimedOutOrCanceled) {
-			hadError = true
-			terminal.Warnf("failed to release lease: %v\n", err)
+		if err != nil {
+			contextTimedOutOrCanceled := errors.Is(err, context.DeadlineExceeded) || errors.Is(err, context.Canceled)
+			var ferr *flaps.FlapsError
+			if errors.As(err, &ferr) && ferr.ResponseStatusCode == http.StatusNotFound {
+				// Having StatusNotFound is expected, if acquiring this entire set is partially failing.
+			} else if !contextWasAlreadyCanceled || !contextTimedOutOrCanceled {
+				hadError = true
+				terminal.Warnf("failed to release lease: %v\n", err)
+			}
 		}
 	}
 	if hadError {