[packages] fix error check in pendingPackagesForInstallation (#1052)

## Summary

The if-condition was ignoring genuine errors

## How was it tested?

```
> rm -rf <project>/.devbox
> cd <project>
# has direnv-enabled, and so this installed the packages that were pending
```

Author: savil

internal/impl/packages.go

@@ -335,6 +335,9 @@ func (d *Devbox) pendingPackagesForInstallation(ctx context.Context) ([]string,
 			ProfileDir: profileDir,
 		})
 		if err != nil {
+			if !errors.Is(err, nix.ErrPackageNotFound) {
+				return nil, err
+			}
 			pending = append(pending, input.Raw)
 		}
 	}