Serial.write(c) not returning what it is supposed to

I'm using a Nano 33 BLE.

[The doc](https://www.arduino.cc/reference/en/language/functions/communication/serial/write/) says:
> write() will return the number of bytes written, though reading that number is optional. Data type: size_t.

But it doesn't seem so, at least when outputting a single byte with USB.

See this test code:
```
void setup() {
Serial.begin(115200);
while (!Serial);

// After the following line, 'count' is supposed to be 1
const int count = Serial.write('A');

// But it isn't
Serial.println(count);
}
```
Console output:
> A65

Start with the provided Nano 33 BLE sketch and trace the Serial.write('A') entry point used for USB output. Compare the returned value with the documented byte count; the issue is resolved when writing one byte reports a count of 1.

Written by the indexing model from the issue text.