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]

Codecov Report

All modified and coverable lines are covered by tests ✅

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

Additional details and impacted files

@@            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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