[skip-changelog] Migrate tests from test_board.py to board_test.go

[MatteoPologruto]

Please check if the PR fulfills these requirements

• The PR has no duplicates (please search among the Pull Requests
  before creating one)
• The PR follows
  our contributing guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• UPGRADING.md has been updated with a migration guide (for breaking changes)

What kind of change does this PR introduce?

Infrastructure enhancement

What is the new behavior?

This PR is a followup to PR #1806
Integration tests that were previously present in test_board.py have been rewritten in board_test.go, without changing their original purpose.
The tests are the following:

• TestBoardList
• TestBoardListWithInvalidDiscovery
• TestBoardListall
• TestBoardListallWithManuallyInstalledPlatform
• TestBoardDetails
• TestBoardDetailsNoFlags
• TestBoardDetailsListProgrammersWithouthFlags
• TestBoardDetailsListProgrammersFlags
• TestBoardSearch
• TestBoardAttachWithoutSketchJson
• TestBoardSearchWithOutdatedCore

Does this PR introduce a breaking change, and is
titled accordingly?

No

---

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[codecov]

Codecov Report

Base: 36.65% // Head: 36.69% // Increases project coverage by +0.04% 🎉

Coverage data is based on head (9967f32) compared to base (2480d93).
Patch has no changes to coverable lines.

❗ Current head 9967f32 differs from pull request most recent head 448a41b. Consider uploading reports for the commit 448a41b to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1847      +/-   ##
==========================================
+ Coverage   36.65%   36.69%   +0.04%     
==========================================
  Files         231      231              
  Lines       19683    19699      +16     
==========================================
+ Hits         7215     7229      +14     
+ Misses      11640    11639       -1     
- Partials      828      831       +3     

Flag	Coverage Δ
unit	36.69% <ø> (+0.04%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
arduino/monitor/monitor.go	41.05% <0.00%> (-4.74%)	⬇️
commands/instances.go	40.04% <0.00%> (+0.40%)	⬆️
arduino/cores/packagemanager/package_manager.go	66.58% <0.00%> (+0.75%)	⬆️
arduino/resources/index.go	52.57% <0.00%> (+12.37%)	⬆️

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[cmaglie]

IMHO we can dramatically improve readability through the use of requirejson let's have a chat about it.