[testbed/datasenders] add missing 0 to nanoseconds calculation (#33321)

**Description:** <Describe what has changed.>

Fixing a bug - the calculation when converting pdata timestamps to
`time` is off in both the `syslog` and `tcpudp` datasenders.
Seconds are calculated correctly by dividing the timestamp by `10^9`,
but in nanosecond calculation the remainder of `timestamp/10^8` is used,
effectively always setting the first decimal in the resulting timestamp
to `0`.

Discovered this while writing some tests against the syslog receiver and
receiving unexpected data in the log body, after identifying the issue a
quick search revealed that the same thing was happening in the tcp/upd
datasender.

**Example:**

`2024-05-31T11:53:54.612287004+02:00` becomes
`2024-05-31T11:53:54.012287004+02:00`

**Link to tracking Issue:** no issue as it's a fairly minor thing that
only affects tests, but can open if required

**Testing:** 
- manual tests
- existing tests

**Documentation:** no additional documentation added.

testbed/datasenders/syslog.go

@@ -89,7 +89,7 @@ func (f *SyslogWriter) GenConfigYAMLStr() string {
 `, f.network, f.GetEndpoint())
 }
 func (f *SyslogWriter) Send(lr plog.LogRecord) error {
-	ts := time.Unix(int64(lr.Timestamp()/1000000000), int64(lr.Timestamp()%100000000)).Format(time.RFC3339Nano)
+	ts := time.Unix(int64(lr.Timestamp()/1_000_000_000), int64(lr.Timestamp()%1_000_000_000)).Format(time.RFC3339Nano)
 	sdid := strings.Builder{}
 	sdid.WriteString(fmt.Sprintf("%s=\"%s\" ", "trace_id", lr.TraceID()))
 	sdid.WriteString(fmt.Sprintf("%s=\"%s\" ", "span_id", lr.SpanID()))

testbed/datasenders/tcpudp.go

@@ -88,7 +88,7 @@ func (f *TCPUDPWriter) GenConfigYAMLStr() string {
 `, f.network, f.GetEndpoint())
 }
 func (f *TCPUDPWriter) Send(lr plog.LogRecord) error {
-	ts := time.Unix(int64(lr.Timestamp()/1000000000), int64(lr.Timestamp()%100000000)).Format(time.RFC3339Nano)
+	ts := time.Unix(int64(lr.Timestamp()/1_000_000_000), int64(lr.Timestamp()%1_000_000_000)).Format(time.RFC3339Nano)
 	sdid := strings.Builder{}
 	sdid.WriteString(fmt.Sprintf("%s=\"%s\" ", "trace_id", traceutil.TraceIDToHexOrEmptyString(lr.TraceID())))
 	sdid.WriteString(fmt.Sprintf("%s=\"%s\" ", "span_id", traceutil.SpanIDToHexOrEmptyString(lr.SpanID())))