build: Update lower bounds to jsonschema v4.15.0, importlib-resources v1.4.0

[matthewfeickert]

Description

Following #1976 (comment) this updates the lower bound of supported jsonschema to v4.15.0 given the discussion that @kratsg opened: https://github.com/orgs/python-jsonschema/discussions/995. This also updates the lower bound on importlib-resources to v1.4.0 as

jsonschema 4.15.0 depends on importlib-resources>=1.4.0; python_version < "3.9"

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• Tests are passing
• "WIP" removed from the title of the pull request
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* Update lower bound of the supported jsonschema versions to v4.15.0 to use the
  required improvements to jsonschema.RefResolver used in PR #1976.
   - c.f. https://github.com/orgs/python-jsonschema/discussions/995
   - Amends PR #1976.
* Update lower bound of the supported importlib-resources versions to v1.4.0 as
  > jsonschema 4.15.0 depends on importlib-resources>=1.4.0; python_version < "3.9"
* Update tests/constraints.txt to use jsonschema==4.15.0 and importlib_resources==1.4.0.

[codecov]

Codecov Report

Base: 98.24% // Head: 98.24% // No change to project coverage 👍

Coverage data is based on head (001ce4c) compared to base (925769a).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1979   +/-   ##
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  Coverage   98.24%   98.24%           
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  Files          68       68           
  Lines        4378     4378           
  Branches      726      726           
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  Hits         4301     4301           
  Misses         45       45           
  Partials       32       32           

Flag	Coverage Δ
contrib	26.58% <ø> (ø)
doctest	60.57% <ø> (ø)
unittests-3.10	96.13% <ø> (ø)
unittests-3.7	96.12% <ø> (ø)
unittests-3.8	96.16% <ø> (ø)
unittests-3.9	96.18% <ø> (ø)

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[kratsg]

We don't need the lower bounds on jsonschema to be 4.15. The change I made is backwards-compatible.

EDIT: It seems that the issue is because of the fact that in the custom schema, we have

{
    "$schema": "http://json-schema.org/draft-06/schema#",
    "$id": "1.1.0/workspace.json",
    "$ref": "defs.json#/definitions/workspace"
}

which is set with base_uri = path/to/custom_schemas/1.1.0 in #1976 . Since there's a $ref and an $id - the $id is being used to add a 1.1.0 to the base_uri when it shouldn't be. So yes, this is a bug in jsonschema that was resolved in 4.15.0.

We could update this to a newer draft for the validator, and this issue won't occur.