fix(avro): return result of wrapped serialize/deserialize when DSM enabled (#15503)

## Description

When DSM is enabled, we aren't returning the function result for
`DatumReader.read` and `DatumWriter.write`. This fixes that to make it
consistent with the default behavior.

## Testing

<!-- Describe your testing strategy or note what tests are included -->

## Risks

<!-- Note any risks associated with this change, or "None" if no risks
-->

## Additional Notes

<!-- Any other information that would be helpful for reviewers -->

Author: robcarlan-datadog

ddtrace/contrib/internal/avro/patch.py

@@ -62,7 +62,7 @@ def _traced_serialize(func, instance, args, kwargs):
     active = pin.tracer.current_span()
 
     try:
-        func(*args, **kwargs)
+        return func(*args, **kwargs)
     finally:
         if active:
             SchemaExtractor.attach_schema_on_span(instance.writers_schema, active, SchemaExtractor.SERIALIZATION)
@@ -80,7 +80,7 @@ def _traced_deserialize(func, instance, args, kwargs):
     active = pin.tracer.current_span()
 
     try:
-        func(*args, **kwargs)
+        return func(*args, **kwargs)
     finally:
         reader = instance
         if active and reader:

releasenotes/notes/avro-dsm-wrapper-fix-e5ec663d7cc7195f.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    avro: Fixes an issue where Avro instrumentation does not return method results when DSM is enabled.