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

When only one of the two time limits is set (e.g. soft_time_limit=42
but no time_limit), the None replacement produced a mixed-type list
["", 42] which triggers an OTel mixed-type attribute warning. Coerce
all values to strings for consistency.

See #2022

Author: DrMeers

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

@@ -76,7 +76,7 @@ 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: