Fix invalid JSON Schema

[aganders3]

This fixes an issue reported on Zulip by @seankmartin. Basically there was a small error in the generated manifest json schema:

❯ check-jsonschema --check-metaschema _schema.json
Schema validation errors were encountered.
  _schema.json::$.definitions.ConfigurationProperty.properties.type.anyOf[1].minItems: True is not of type 'integer'
  _schema.json::$.definitions.Draft06JsonSchema.properties.type.anyOf[1].minItems: True is not of type 'integer'
  _schema.json::$.definitions.Draft07JsonSchema.properties.type.anyOf[1].minItems: True is not of type 'integer'

The root of the problem is here, where min_items is set to True instead of an integer.
https://github.com/napari/npe2/blob/80ca5feb501dd25d36ecf1313f94d80366d25b8e/src/npe2/manifest/contributions/_json_schema.py#L24C3-L24C3

The first commit here adds a check of the schema in CI using check-jsonschema. Then the second commit should fix the underlying issue.

cc: @nclack

[aganders3]

The first commit here adds a check of the schema in CI using check-jsonschema. Then the second commit should fix the underlying issue.

See this CI run for the expected new failure

[codecov]

Codecov Report

Merging #309 (795336a) into main (80ca5fe) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main      #309   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
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  Files           37        37           
  Lines         2818      2818           
=========================================
  Hits          2818      2818           

Files Changed	Coverage Δ
src/npe2/manifest/contributions/_json_schema.py	100.00% <100.00%> (ø)

[aganders3]

Also note there is a double-import error when running python -m npe2.manifest.schema to generate the schema. I don't think it's causing problems, but I can open another issue for discussion on that.

<frozen runpy>:128: RuntimeWarning: 'npe2.manifest.schema' found in sys.modules after import of package 'npe2.manifest', but prior to execution of 'npe2.manifest.schema'; this may result in unpredictable behaviour

[nclack]

Thanks! I'll merge tomorrow if there are no objections.