fix: fix test of root span to match what is being set (#2494)

# What does this PR do?

I get errors when trying to query spans. It appears to be a result of
traces being inserted where there is no root_span_id which causes a
pydantic validation error on trying to load the data for a query
response (and in any case having no span referenced undermines the
purpose of the trace). The root cause as far as I can see is an invalid
test in the code that inserts the trace, where it is testing for the
string "true" against an object set to the python value True.

<!-- If resolving an issue, uncomment and update the line below -->
Closes #2493 

## Test Plan
<!-- Describe the tests you ran to verify your changes with result
summaries. *Provide clear instructions so the plan can be easily
re-executed.* -->
With this change I can query spans.

Signed-off-by: Gordon Sim <gsim@redhat.com>

llama_stack/providers/inline/telemetry/meta_reference/sqlite_span_processor.py

@@ -14,6 +14,8 @@ from opentelemetry.sdk.trace import SpanProcessor
 from opentelemetry.trace import Span
 from opentelemetry.trace.span import format_span_id, format_trace_id
 
+from llama_stack.providers.utils.telemetry.tracing import LOCAL_ROOT_SPAN_MARKER
+
 
 class SQLiteSpanProcessor(SpanProcessor):
     def __init__(self, conn_string):
@@ -124,7 +126,7 @@ class SQLiteSpanProcessor(SpanProcessor):
                 (
                     trace_id,
                     service_name,
-                    (span_id if span.attributes.get("__root_span__") == "true" else None),
+                    (span_id if span.attributes.get(LOCAL_ROOT_SPAN_MARKER) else None),
                     datetime.fromtimestamp(span.start_time / 1e9, UTC).isoformat(),
                     datetime.fromtimestamp(span.end_time / 1e9, UTC).isoformat(),
                 ),