fix(celery): coerce timelimit values to strings in span attributes (#4361)

Author: DrMeers

CHANGELOG.md

@@ -73,6 +73,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- `opentelemetry-instrumentation-celery`: Coerce timelimit values to strings in `set_attributes_from_context()` to prevent mixed-type span attribute warning
+  ([#4361](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4361))
 - `opentelemetry-docker-tests`: Replace deprecated `SpanAttributes` from `opentelemetry.semconv.trace` with `opentelemetry.semconv._incubating.attributes`
  ([#4339](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4339))
 - `opentelemetry-instrumentation-confluent-kafka`: Skip `recv` span creation when `poll()` returns no message or `consume()` returns an empty list, avoiding empty spans on idle polls

instrumentation/opentelemetry-instrumentation-celery/src/opentelemetry/instrumentation/celery/utils.py

@@ -65,7 +65,7 @@ def set_attributes_from_context(span, context):
             if value in [(None, None), [None, None]]:
                 continue
             if None in value:
-                value = ["" if tl is None else tl for tl in value]
+                value = ["" if tl is None else str(tl) for tl in value]
 
         # Skip `retries` if it's value is `0`
         if key == "retries" and value == 0: