Fix panic in otelhttptrace

Wait100Continue trace event is sent here before "http.receive" phase which results with a panic

instrumentation/net/http/httptrace/otelhttptrace/clienttrace.go

@@ -370,7 +370,7 @@ func (ct *clientTracer) got100Continue() {
 func (ct *clientTracer) wait100Continue() {
 	span := ct.root
 	if ct.useSpans {
-		span = ct.span("http.receive")
+		span = ct.span("http.send")
 	}
 	span.AddEvent("GOT 100 - Wait")
 }

instrumentation/net/http/httptrace/otelhttptrace/test/clienttrace_test.go

@@ -15,6 +15,7 @@
 package test
 
 import (
+	"bytes"
 	"context"
 	"net/http"
 	"net/http/httptest"
@@ -504,3 +505,35 @@ func TestHTTPRequestWithTraceContext(t *testing.T) {
 	require.Equal(t, parent.SpanContext().TraceID(), getconn.SpanContext().TraceID())
 	require.Equal(t, parent.SpanContext().SpanID(), getconn.Parent().SpanID())
 }
+
+func TestHTTPRequestWithExpect100Continue(t *testing.T) {
+	fixture := prepareClientTraceTest(t)
+
+	ctx, span := otel.Tracer("oteltest").Start(context.Background(), "root")
+	ctx = httptrace.WithClientTrace(ctx, otelhttptrace.NewClientTrace(ctx))
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, fixture.URL, bytes.NewReader([]byte("test")))
+	require.NoError(t, err)
+
+	// Set Expect: 100-continue
+	req.Header.Set("Expect", "100-continue")
+	resp, err := fixture.Client.Do(req)
+	require.NoError(t, err)
+	require.NoError(t, resp.Body.Close())
+	span.End()
+
+	require.Len(t, fixture.SpanRecorder.Ended(), 5)
+
+	// http.send should contains "GOT 100 - Wait" event
+	send, ok := getSpanFromRecorder(fixture.SpanRecorder, "http.send")
+	require.True(t, ok)
+
+	found := false
+	for _, v := range send.Events() {
+		if v.Name == "GOT 100 - Wait" {
+			found = true
+			break
+		}
+	}
+	require.True(t, found)
+}