arduino-cli throws invalid number literal on core update index

[duglah]

Hello everybody,

currently the package_azureboard_index.json is broken, because it has a whitespace in the size literal, so the arduino-cli will throw a

Error updating index: invalid package index in https://raw.githubusercontent.com/VSChina/azureiotdevkit_tools/master/package_azureboard_index.json: json: invalid number literal, trying to unmarshal ""3788484 "" into Number

when you try to update the index of cores on MacOS with arduino-cli 0.17.0.

Steps to reproduce:

1. Install arduino-cli, see the offical arduino-cli installation guide
2. Create a configuration file: `arduino-cli config init``
3. Open config file and add https://github.com/VSChina/azureiotdevkit_tools/blob/master/package_azureboard_index.json as additional url:
   Example:

board_manager:
  additional_urls: [https://raw.githubusercontent.com/duglah/azureiotdevkit_tools/master/package_azureboard_index.json]

4. Run arduino-cli core update-index

[silvanocerza]

This kind of issues with custom indexes will be mitigated with the next release of the Arduino CLI, the bad index won't be loaded but it won't break the rest of the Arduino CLI so it remains usable. Obviously it won't be possible to install cores/platforms from the bad index since it's not loaded at all.
That mitigation is already available in the nightlies if you want to try it.

To avoid this kind of issues in the future I suggest using Arduino Lint, it checks for irregularities and errors in several types of Arduino projects including indexes. We also made a Github Action arduino/arduino-lint-action to automatically run it on all PRs.