[chore] close http responses and preallocate slices (#24926)

These changes only affect tests.

receiver/signalfxreceiver/receiver_test.go

@@ -344,6 +344,7 @@ func Test_sfxReceiver_handleReq(t *testing.T) {
 
 			resp := w.Result()
 			respBytes, err := io.ReadAll(resp.Body)
+			defer resp.Body.Close()
 			assert.NoError(t, err)
 
 			var bodyStr string
@@ -521,6 +522,7 @@ func Test_sfxReceiver_handleEventReq(t *testing.T) {
 			resp := w.Result()
 			respBytes, err := io.ReadAll(resp.Body)
 			assert.NoError(t, err)
+			defer resp.Body.Close()
 
 			var bodyStr string
 			assert.NoError(t, json.Unmarshal(respBytes, &bodyStr))
@@ -600,6 +602,7 @@ func Test_sfxReceiver_TLS(t *testing.T) {
 
 	resp, err := client.Do(req)
 	require.NoErrorf(t, err, "should not have failed when sending to signalFx receiver %v", err)
+	defer resp.Body.Close()
 	assert.Equal(t, http.StatusOK, resp.StatusCode)
 	t.Log("SignalFx Request Received")
 
@@ -664,6 +667,7 @@ func Test_sfxReceiver_DatapointAccessTokenPassthrough(t *testing.T) {
 			resp := w.Result()
 			respBytes, err := io.ReadAll(resp.Body)
 			assert.NoError(t, err)
+			defer resp.Body.Close()
 
 			var bodyStr string
 			assert.NoError(t, json.Unmarshal(respBytes, &bodyStr))
@@ -742,6 +746,7 @@ func Test_sfxReceiver_EventAccessTokenPassthrough(t *testing.T) {
 			resp := w.Result()
 			respBytes, err := io.ReadAll(resp.Body)
 			assert.NoError(t, err)
+			defer resp.Body.Close()
 
 			var bodyStr string
 			assert.NoError(t, json.Unmarshal(respBytes, &bodyStr))

receiver/signalfxreceiver/signalfxv2_event_to_logdata_test.go

@@ -96,7 +96,7 @@ func TestSignalFxV2EventsToLogData(t *testing.T) {
 }
 
 func mapToEventProps(m map[string]interface{}) []*sfxpb.Property {
-	var out []*sfxpb.Property
+	out := make([]*sfxpb.Property, 0, len(m))
 	for k, v := range m {
 		var pval sfxpb.PropertyValue