chore: add version checking to django channels (#15484)

## Description

<!-- Provide an overview of the change and motivation for the change -->

Quick fix for version checking for django channels, to fix
`AttributeError` when `__version__` not found

## 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: quinna-h

ddtrace/contrib/internal/django/patch.py

@@ -473,7 +473,8 @@ def _(m):
     def _(m):
         import channels
 
-        channels_version = parse_version(channels.__version__)
+        channels_version_str = getattr(channels, "__version__", "")
+        channels_version = parse_version(channels_version_str)
         if channels_version >= parse_version("3.0"):
             # ASGI3 is only supported in channels v3.0+
             trace_utils.wrap(m, "URLRouter.__init__", unwrap_views)