All format test cases should be under the `format` directory.

[big-andy-coates]

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fixes: https://github.com/creek-service/json-schema-validation-comparison/issues/190

Currently, there exists an ecma regex test case, that uses "format": "regex", but which does not live under the optional/format directory.

My understanding was that all tests that require format validation from implementations where under the optional/format directory. (As per point #2 under the Additional Assumptions section of the docs).

Having this one test case outside of the directory complicates the implementations of all test runners and the need to turn on format validation for this one test case isn't even documented.

As such, this change moves the test requiring format under the optional/format directory.

This change was prompted by: https://github.com/creek-service/json-schema-validation-comparison/issues/190