* move Instance variables to class variables. Since the object in que…

…stion will be a singelton. This will resolve open-telemetry#2029 where multiple calls to the instrumentation will assign Null values.

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

@@ -113,10 +113,11 @@ def keys(self, carrier):
 
 
 class CeleryInstrumentor(BaseInstrumentor):
+    metrics = None
+    task_id_to_start_time = {}
+
     def __init__(self):
         super().__init__()
-        self.metrics = None
-        self.task_id_to_start_time = {}
 
     def instrumentation_dependencies(self) -> Collection[str]:
         return _instruments