fix: handle combined oneOf types

[Spence1115]

Summary

When a schema produces multiple oneOf statements for a key, we are nesting them when we should be combining them

Example

        {
          "form": [
            {
              "value": "John Doe",
            },
            {
              "value": [],
            },
            {
              "value": null,
            },
          ]
        },
        {
          "form": null
        },
        {
          "form": [
            {
              "value": false,
            },
            {
              "value": ["First", "Second"],
            },
            {
              "value": 3,
            },
          ]
        }

Before

                              value:
                                oneOf:
                                - oneOf:
                                  - type: string
                                  - type: array
                                    items: {}
                                - oneOf:
                                  - type: boolean
                                  - type: array
                                    items:
                                      type: string
                                  - type: integer

Now

                              value:
                                oneOf:
                                - type: string
                                - type: array
                                  items: {}
                                - type: boolean
                                - type: array
                                  items:
                                    type: string
                                - type: integer

Fixes #290

[codecov]

Codecov Report

❌ Patch coverage is 74.19355% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.44%. Comparing base (70ff4b2) to head (8e0a545).

Files with missing lines	Patch %	Lines
lib/rspec/openapi/schema_builder.rb	74.19%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #291      +/-   ##
==========================================
- Coverage   98.48%   97.44%   -1.04%     
==========================================
  Files          20       20              
  Lines         724      744      +20     
  Branches      184      192       +8     
==========================================
+ Hits          713      725      +12     
- Misses         11       19       +8     

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[Spence1115]

Doesn't seem to be pulling the latest results from codecov