fix(celery): coerce non-string values to str in CeleryGetter.get()

Celery's Context object copies all message properties as instance attrs,
including numeric fields like timelimit. CeleryGetter.get() wrapped these
in a tuple but didn't convert to str, causing TextMapPropagators to crash
with "TypeError: expected string or bytes-like object, got 'int'" when
calling re.split() in TraceState.from_header().

Coerce non-string, non-iterable values to str before wrapping in a tuple.

Fixes #4359

Signed-off-by: alliasgher <alliasgher123@gmail.com>

Author: alliasgher

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

@@ -104,8 +104,14 @@ def get(self, carrier, key):
         value = getattr(carrier, key, None)
         if value is None:
             return None
-        if isinstance(value, str) or not isinstance(value, Iterable):
-            value = (value,)
+        if isinstance(value, str):
+            return (value,)
+        if not isinstance(value, Iterable):
+            # Coerce non-string, non-iterable values (e.g. int from Celery
+            # task attributes like timelimit) to str so that propagators
+            # such as TraceContext don't crash with a TypeError when calling
+            # re.split() on the value.
+            return (str(value),)
         return value
 
     def keys(self, carrier):