Fix psych disallowedclass error in ruby 3.1

[ipepe]

Fixes #249 by adding Date to permitted_classes of YAML.safe_load in RSpec::OpenAPI::SchemaFile#read.

Changes

• allow Date and Time when reading YAML schema files
• add regression test for SchemaFile

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.27%. Comparing base (099958e) to head (ac389d0).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #256   +/-   ##
=======================================
  Coverage   97.26%   97.27%           
=======================================
  Files          20       20           
  Lines         658      660    +2     
  Branches      148      148           
=======================================
+ Hits          640      642    +2     
  Misses         18       18           

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[rhiroe]

[nits]
require 'yaml' also loads Date. Time is available without requiring anything explicitly.

[rhiroe]

[imho]
How about adding unquoted dates or times to the OpenAPI schema in spec/apps/ instead of writing tests for the private method?

What should be tested is not whether unquoted dates or times are loaded, but whether the resulting OpenAPI schema output is correct—and whether it can be successfully loaded.