Fix Callback.handle_event crash on OTel metrics with dict tag values

[vatsrahul1001]

Summary

Triggerer crashes on the next deadline async callback when OpenTelemetry metrics are enabled:

File ".../airflow/jobs/triggerer_job_runner.py", line 659, in handle_events
    Trigger.submit_event(...)
File ".../airflow/models/callback.py", line 234, in handle_event
    Stats.incr(**self.get_metric_info(status, self.output))
File ".../airflow/_shared/observability/metrics/otel_logger.py", line 211, in incr
    counter.add(count, attributes=tags)
File ".../opentelemetry/sdk/metrics/.../view_instrument_match.py", line 105
    aggr_key = frozenset(attributes.items())
TypeError: unhashable type: 'dict'

Root cause

Callback.get_metric_info builds the metric tags dict directly from the callback's result and self.data (which includes kwargs). Both are frequently dicts — for deadline async callbacks the result is the user callback's return value, and kwargs is the captured callback kwargs.

When the metrics backend is OpenTelemetry, the SDK builds the aggregation key as frozenset(attributes.items()), which raises TypeError: unhashable type: 'dict' if any value is unhashable (dict, list, set). Result: triggerer crash, stalled triggers.

The bug is metrics-backend-dependent: statsd accepts non-primitive tag values without complaint, so OSS users running the default statsd never see it. OpenTelemetry backends hit it consistently — surfaced by Astronomer Astro Cloud, but affects any OSS deployment that enables [metrics] otel_*.

Reproduces against 3.2.1 and main — not a 3.2.x regression.

Fix

Sanitize tag values to primitives before returning from get_metric_info. Keep str | int | float | bool | None as-is; JSON-stringify anything else using default=str so values like datetime fall back cleanly instead of raising.

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

• Yes — Claude Code (Opus 4.7)

Generated-by: Claude Code (Opus 4.7) following the guidelines

[github-actions]

Hi maintainer, this PR was merged without a milestone set.
We've automatically set the milestone to Airflow 3.2.3 based on: backport label targeting v3-2-test
If this milestone is not correct, please update it to the appropriate milestone.

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[github-actions]

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Status	Branch	Result
❌	v3-2-test

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