Certificate upload fails if Serial Monitor/Plotter is open

[per1234]

Describe the bug

The Arduino IDE includes an "Upload SSL Root Certificates"" tool that can be used to upload SSL certificates to the Wi-Fi radio module of Arduino boards such as the MKR WiFi 1010 and Nano 33 IoT.

🐛 If the Serial Monitor or Serial Plotter is open when a certificate upload is attempted, it fails.

To Reproduce

1. Connect an Arduino board that has a u-blox NINA-W102 module to your computer via the USB cable.
2. Select the board and port in the IDE.
3. Open the Arduino IDE Serial Monitor (Tools > Serial Monitor).
4. Select Tools > Upload SSL Root Certificates from the Arduino IDE menus.
5. Select a certificate and the board in the Upload SSL Root Certificates dialog.
6. Click the Upload button.
7. Wait for the Upload process to finish.

🐛 The process fails without any indication of the cause:

⚠ Upload failed. Please try again.

Expected behavior

Automatically close the serial port as needed, reopening it in Serial Monitor once done, similar to how it is handled during the Upload process.

Desktop

• OS: Windows 10
• Version: 2.0.0-rc3-snapshot.35e5da5
  Date: 2022-01-13T17:15:54.562Z
  CLI Version: 0.20.2 [13783819]

Additional context

The IDE's "WiFi101 / WiFiNINA Firmware Updater"" tool had the same problem (#684), which was fixed already by #688. Perhaps that same fix can be applied to the "Upload SSL Root Certificates"" tool as well.

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Additional reports:

• https://forum.arduino.cc/t/ssl-certificate-update-failed/1062117