fix: Add null checks for span filtering attributes

[CagriYonca]

Reproduced and fixed the errors below for the case where http.host is None

• Before the fix

2026-03-11 13:45:01,464: 14999 DEBUG instana: Flask(blinker): Applying flask before/after instrumentation funcs
2026-03-11 13:45:01,465: 14999 DEBUG instana: urllib3 _collect_kvs error: 
Traceback (most recent call last):
  File "/Users/cagriyonca/Projects/pep0249/python-sensor/src/instana/instrumentation/urllib3.py", line 58, in _collect_kvs
    url = kvs["host"] + ":" + str(kvs["port"]) + kvs["path"]
          ~~~~~~~~~~~~^~~~~
TypeError: unsupported operand type(s) for +: 'NoneType' and 'str'
127.0.0.1 - - [11/Mar/2026 13:45:01] "GET /test-urllib3-none-host HTTP/1.1" 500 -
2026-03-11 13:45:01,859: 14999 DEBUG instana: report_data_payload: Instana host agent connection error (<class 'TypeError'>)
Traceback (most recent call last):
  File "/Users/cagriyonca/Projects/pep0249/python-sensor/src/instana/agent/host.py", line 287, in report_data_payload
    response = self.report_spans(payload)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/cagriyonca/Projects/pep0249/python-sensor/src/instana/agent/host.py", line 346, in report_spans
    filtered_spans = self.filter_spans(payload.get("spans", []))
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/cagriyonca/Projects/pep0249/python-sensor/src/instana/agent/host.py", line 389, in filter_spans
    if self.__is_endpoint_ignored(attributes_to_check):
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/cagriyonca/Projects/pep0249/python-sensor/src/instana/agent/host.py", line 411, in __is_endpoint_ignored
    if any(
       ^^^^
  File "/Users/cagriyonca/Projects/pep0249/python-sensor/src/instana/agent/host.py", line 412, in <genexpr>
    matches_rule(rule.get("attributes", []), span_attributes)
  File "/Users/cagriyonca/Projects/pep0249/python-sensor/src/instana/util/span_utils.py", line 42, in matches_rule
    if match_key_filter(span_value, rule_value, match_type):
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/cagriyonca/Projects/pep0249/python-sensor/src/instana/util/span_utils.py", line 58, in match_key_filter
    elif match_type == "contains" and rule_value in span_value:
                                      ^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: argument of type 'NoneType' is not iterable

• After the fix

2026-03-11 14:05:28,947: 20582 DEBUG instana: Flask(blinker): Applying flask before/after instrumentation funcs
127.0.0.1 - - [11/Mar/2026 14:05:28] "GET /test-urllib3-none-host HTTP/1.1" 200 -
2026-03-11 14:05:29,399: 20582 DEBUG instana: Reporting 2 spans

[sonarqubecloud]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[pvital]

It looks good to me.