X-B3-Sampled: 0 alone does not disable the tracing

Describe your environment
fastapi>=0.70.0
uvicorn[standard]>=0.15.0
opentelemetry-api==1.8.0
opentelemetry-sdk==1.8.0
opentelemetry-exporter-zipkin==1.8.0
opentelemetry-propagator-b3==1.8.0
opentelemetry-instrumentation-fastapi==0.27b0

Steps to reproduce
Start server

from opentelemetry import trace
from opentelemetry.exporter.zipkin.json import ZipkinExporter
from opentelemetry.sdk.trace import TracerProvider
from opentelemetry.sdk.resources import Resource
from opentelemetry.sdk.trace.export import BatchSpanProcessor
from fastapi import FastAPI
from opentelemetry.instrumentation.fastapi import FastAPIInstrumentor
from opentelemetry.propagate import set_global_textmap
from opentelemetry.propagators.b3 import B3MultiFormat
import uvicorn

app = FastAPI()

tracer = trace.get_tracer(__name__)
zipkin_exporter = ZipkinExporter(
    endpoint="http://127.0.0.1:9411/api/v2/spans",
)
span_processor = BatchSpanProcessor(zipkin_exporter)
trace_provider = TracerProvider(resource=Resource.create({"service.name": "open-telemetry-test"}))
trace_provider.add_span_processor(span_processor)
trace.set_tracer_provider(trace_provider)

set_global_textmap(B3MultiFormat())

@app.get('/hello')
def hello():
    with tracer.start_as_current_span("hello"):
        return {'hello': 'there'}

FastAPIInstrumentor.instrument_app(app,tracer_provider=trace_provider)

if __name__ == "__main__":
    uvicorn.run(app, host="0.0.0.0", port=8000)

Test

import requests
requests.get("http://localhost:8000/hello", headers={'X-B3-Sampled': '0'})

What is the expected behavior?
No trace log to Zipkin
https://github.com/openzipkin/b3-propagation

What is the actual behavior?
Trace still log to Zipkin

Additional context
Zipkin docker image: ghcr.io/openzipkin/zipkin-slim:2.23

If has other B3 headers, X-B3-Sampled': '0' works

import requests
from opentelemetry.sdk.trace import id_generator
requests.get("http://localhost:8000/hello", headers={
    'X-B3-TraceId': "{:032x}".format(id_generator.RandomIdGenerator().generate_trace_id()),
    'X-B3-ParentSpanId': "{:016x}".format(id_generator.RandomIdGenerator().generate_span_id()),
    'X-B3-SpanId': "{:016x}".format(id_generator.RandomIdGenerator().generate_span_id()),
    'X-B3-Sampled': '0'
})

Reproduce the request against the FastAPI example using only the X-B3-Sampled: 0 header, then compare it with the request containing the other B3 headers. Start by tracing how B3MultiFormat and FastAPIInstrumentor handle incoming headers. Done means a request with X-B3-Sampled: 0 alone produces no trace in Zipkin.