Use augmented assignment statements (#797)

Fixes #796

Author: ocelotl

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

@@ -160,7 +160,7 @@ def collect_request_attributes(scope):
     if query_string and http_url:
         if isinstance(query_string, bytes):
             query_string = query_string.decode("utf8")
-        http_url = http_url + ("?" + urllib.parse.unquote(query_string))
+        http_url += "?" + urllib.parse.unquote(query_string)
 
     result = {
         SpanAttributes.HTTP_SCHEME: scope.get("scheme"),