Fix JSON Schema

[k1LoW]

ref: #646

SSIA.

[github-actions]

Code Metrics Report

	main (f542f95)	#650 (30c4592)	+/-
Coverage	55.6%	54.1%	-1.6%
Code to Test Ratio	1:0.4	1:0.4	-0.1
Test Execution Time	4m25s	4m26s	+1s

Details

  |                     | main (f542f95) | #650 (30c4592) |  +/-  |
  |---------------------|----------------|----------------|-------|
- | Coverage            |          55.6% |          54.1% | -1.6% |
  |   Files             |             52 |             52 |     0 |
  |   Lines             |           4798 |           4807 |    +9 |
- |   Covered           |           2671 |           2602 |   -69 |
- | Code to Test Ratio  |          1:0.4 |          1:0.4 |  -0.1 |
  |   Code              |          10390 |          10422 |   +32 |
  |   Test              |           4342 |           4342 |     0 |
- | Test Execution Time |          4m25s |          4m26s |   +1s |

Code coverage of files in pull request scope (51.5% → 51.9%)

Files	Coverage	+/-
schema/json.go	83.6%	-1.8%
schema/schema.go	39.8%	0.0%

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Reported by octocov