Tools: Improve gitea utils function optional paramenter handling

Two fixes/improvements to `gitea_json_issue_events_filter()`:
- The `username` parameter would be optional, but not setting it would
  make the function do nothing. Ignore it if not set.
- Not passing `event_type` (and not passing `labels`) would make the
  function do nothing. It wasn't optional strictly speaking but the
  default was an empty set, which is more or less the same. Make it
  properly optional so not specifying an event-type will return events
  of any type.

tools/triage/gitea_utils.py

@@ -162,7 +162,7 @@ def gitea_json_issue_events_filter(
         date_end: datetime.datetime | None = None,
         username: str | None = None,
         labels: set[str] | None = None,
-        event_type: set[str] = set(),
+        event_type: set[str] | None = None,
 ) -> list[dict[str, Any]]:
     """
     Filter all comments and events on the issue list.
@@ -189,12 +189,12 @@ def gitea_json_issue_events_filter(
         if not event:
             continue
 
-        if not event["user"] or event["user"]["username"] != username:
+        if username and (not event["user"] or event["user"]["username"] != username):
             continue
 
         if labels and event["type"] == "label" and event["label"]["name"] in labels:
             pass
-        elif event["type"] in event_type:
+        elif not event_type or event["type"] in event_type:
             pass
         else:
             continue