test: cover ISO8601 date values accepted by Python 3.11 datetime module

[jvtm]

Python 3.11 datetime module allows additional ISO8601 date, time and date-time formats that are not RFC3339 5.6 compliant.

This change adds tests for invalid date values that are at the moment allowed by at least Python jsonschema library as valid date sttrings.

Looks like date-time and time test cases already cover at least some values that are valid by ISO8601 but not by RFC3339 section 5.6.

See:

• https://docs.python.org/3/whatsnew/3.11.html#datetime
• https://github.com/python/cpython/commit/1303f8c927
• https://docs.python.org/3.11/library/datetime.html#datetime.date.fromisoformat
• https://www.rfc-editor.org/rfc/rfc3339#section-5.6

PR sent to jsonschema library python-jsonschema/jsonschema#1076.

[jvtm]

Need to fix few of these:

Description is too long (keep it to less than 70 chars).

Done, shortened the longest descriptions.