Fix DateTimeSensorAsync crash on templated target_time with start_from_trigger

[burakcoleman]

DateTimeSensorAsync.__init__ computes start_trigger_args.trigger_kwargs["moment"] by calling
timezone.parse(self.target_time) at Dag-parse time, before Jinja templating has run. target_time
is a documented template field (e.g. "{{ data_interval_end.tomorrow().replace(hour=1) }}"), so a
templated value raises a raw pendulum.parsing.exceptions.ParserError there, crashing parsing of the
entire Dag file, not just the one task.

This can't be fixed by moving the parse into execute(): when start_from_trigger=True, the scheduler
defers the task straight from TaskInstance.defer_task() using the pre-computed self.task.start_trigger_args
— execute() never runs for this path. So the value genuinely has to be resolved in __init__, the same
constraint TimeSensor hit in #69610.

Fix: catch the parse failure and raise a clear ValueError explaining that start_from_trigger=True
requires a static target_time, instead of letting the raw ParserError propagate and take down the
whole Dag file. Static/ISO target_time values are unaffected and keep working exactly as before.

Added tests covering both the static-time (still works) and templated-time (now raises a clear,
task-scoped error instead of crashing Dag parsing) cases.

closes: #70284
Related: #69610

Was generative AI tooling used to co-author this PR?

• Yes — Claude Code

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[raphaelauv]

same than #70310 ?