Updated typehints for _collect callback.

Added Changelog entry for the public API

Author: JP-MY

.changelog/4863.added

@@ -0,0 +1 @@
+`opentelemetry-sdk`: add `add_metric_reader` / `remove_metric_reader` public APIs to register / unregister metric readers at runtime.

opentelemetry-sdk/src/opentelemetry/sdk/metrics/_internal/export/__init__.py

@@ -229,7 +229,7 @@ def __init__(
                 AggregationTemporality,
             ],
             Iterable[opentelemetry.sdk.metrics.export.Metric],
-        ] = None
+        ] | None = None
 
         self._instrument_class_temporality = {
             _Counter: AggregationTemporality.CUMULATIVE,
@@ -373,7 +373,7 @@ def _set_collect_callback(
                 AggregationTemporality,
             ],
             MetricsData,
-        ],
+        ] | None,
     ) -> None:
         """This function is internal to the SDK. It should not be called or overridden by users"""
         self._collect = func