Add JSON.jl 1.x compatibility

[fromelicks]

Closes #99, and technically julia-vscode/LanguageServer.jl#1389 too.

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• End-user documentation check. If this PR requires end-user documentation in the Julia VS Code extension docs, please add that at https://github.com/julia-vscode/docs.
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Related:

• Add JSON.jl 1.x compatibility DebugAdapter.jl#125
• CompatHelper: bump compat for JSON to 1, (keep existing compat) LanguageServer.jl#1364
• Add JSON.jl 1.x to compat LanguageServer.jl#1464

[codecov]

Codecov Report

❌ Patch coverage is 94.44444% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 92.20%. Comparing base (2f1bc7f) to head (6b1485d).
⚠️ Report is 65 commits behind head on main.

Files with missing lines	Patch %	Lines
src/jsoncompat.jl	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #118      +/-   ##
==========================================
+ Coverage   90.59%   92.20%   +1.61%     
==========================================
  Files           5        5              
  Lines         287      539     +252     
==========================================
+ Hits          260      497     +237     
- Misses         27       42      +15     

Flag	Coverage Δ
unittests	92.20% <94.44%> (+1.61%)	⬆️

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[fromelicks]

@davidanthoff or @pfitzseb, could you possibly review, please?

[pfitzseb]

Don't strictly need to run on JSON 1.x here since that gets picked up by the normal tests, but can't hurt I guess.

[davidanthoff]

We shouldn't put extra jobs into that workflow, that is really a template for the underlying shared workflow. We could use a second workflow file for this, or I'm also still thinking whether there is a good way to handle this natively in the testitem-workflow story.

I'll open a new PR doing whatever I come up with :)