Fix is_confidential property

[olethanh]

This was causing an error in the monitor payment task

AttributeError: 'FunctionEnvironment' object has no attribute 'trusted_execution'
  File "aleph/vm/utils/__init__.py", line 90, in run_and_log_exception
    return await coro
  File "aleph/vm/orchestrator/tasks.py", line 154, in monitor_payments
    executions = [execution for execution in executions if execution.is_confidential]
  File "aleph/vm/orchestrator/tasks.py", line 154, in <listcomp>
    executions = [execution for execution in executions if execution.is_confidential]
  File "aleph/vm/models.py", line 113, in is_confidential
    return True if self.message.environment.trusted_execution else False

To reproduce

Run a program so it's in the execution lists for example a permanent one, Then wait for the monitory_payments task to run

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 61.53%. Comparing base (ff6c119) to head (c3e065d). Report is 4 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #674 +/- ## ========================================== + Coverage 61.43% 61.53% +0.10% ========================================== Files 68 68 Lines 5997 5997 Branches 635 635 ========================================== + Hits 3684 3690 +6 + Misses 2158 2153 -5 + Partials 155 154 -1 ```

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