Add test for extended year in date-time format

[sangamon]

JSON Schema specifies RFC 3339 format for date-time format. Quite some implementation languages/standard libraries (e.g. Java java.time.OffsetDateTime) rather implement ISO 8601 parsing, covering "extended year" values. Consequently, validators that derive their date-time validation from these parsers will accept such values. E.g., according to json-schema-validation-comparison as of 2025-09-29 (commit 01a80d0), the following JVM implementations are affected: DevHarrel, Everit, Justify, Medeia, SchemaFriend, Skema. It would be nice to have an "authoritative" canary for this issue. A potential test case for this, to be added to date-time.json scenarios:

{
  "description": "invalid extended year",
  "data": "+11963-06-19T08:30:06.283185Z",
  "valid": false
}

[jdesrosiers]

Sounds good. A PR would be welcome if you're willing and able.

[jdesrosiers]

Thank you!