Support for openapi 3.0.4

Summary

OpenAPI specs preview doesn't seems to work for specific 3.0.4 version (working well for 3.0.3 and 3.1.0).

Steps to reproduce

• Create an basic openapi file using version 3.0.4 openapi spec version. You can use the following snippet

openapi: 3.0.4
info:
    title: Test
    version: 1.0.0

paths:
    /test:
        get:
            responses:
                400:
                    description: Bad request

Example Project

See example project

What is the current bug behavior?

Trying previewing the file fails with the following error message:

Unable to render this definition
The provided definition does not specify a valid version field.

Please indicate a valid Swagger or OpenAPI version field. Supported version fields are swagger: "2.0" and those that match openapi: 3.x.y (for example, openapi: 3.1.0).

What is the expected correct behavior?

Preview of the file should work well

Relevant logs and/or screenshots

Output of checks

This bug happens on GitLab.com

Results of GitLab environment info

Expand for output related to GitLab environment info

(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:env:info`)

(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production`)

Results of GitLab application Check

Expand for output related to the GitLab application check

(For installations with omnibus-gitlab package run and paste the output of:
sudo gitlab-rake gitlab:check SANITIZE=true)
(For installations from source run and paste the output of:
sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true)
(we will only investigate if the tests are passing)

Possible fixes

Patch release information for backports

If the bug fix needs to be backported in a patch release to a version under the maintenance policy, please follow the steps on the patch release runbook for GitLab engineers.

Refer to the internal "Release Information" dashboard for information about the next patch release, including the targeted versions, expected release date, and current status.

High-severity bug remediation

To remediate high-severity issues requiring an internal release for single-tenant SaaS instances, refer to the internal release process for engineers.