[BUG] Unrecognized token 'openapi' on Windows boxes

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• [] Have you searched for related issues/PRs?
• [] What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

Using openapi generator gradle plugin 5.1.1.
Spec is validated by the online tools.

On Mac machines and/orr Docker linux containers, it works perfectly.

On windows machines, I have this:

 ./gradlew build

> Task :openApiValidate FAILED
Validating spec /Users/az02277-dev/builds/shared/api-springboot-java/src/main/resources/openapi/api-v1.0.yaml
failed to read resource listing
com.fasterxml.jackson.core.JsonParseException: Unrecognized token 'openapi': was expecting (JSON String, Number, Array, Object or token 'null', 'true' or 'false')
 at [Source: (String)"openapi: "3.0.0"

If I use an openapi version which does not exist (3.1.0 for instance) the output is similar, no matter which platform I use.

openapi-generator version

5.x.x versions have the issue
4.3.1 works just fine

OpenAPI declaration file content or url

Tried with several spec files, so I don't think the content is relevant.
However, if you can't reproduce it, I could provide the spec.

Generation Details

Openapi generator plugin for gradle with java 11 OpenJdk

Steps to reproduce

On a Windows platform:
./gradlew openApiGenerate

Related issues/PRs

Suggest a fix

Start with the Gradle plugin's openApiValidate and openApiGenerate tasks, reproducing the failure on Windows with openapi-generator 5.x and Java 11. Compare the behavior with version 4.3.1 and the reported Mac or Docker results; done means a valid OpenAPI YAML file is accepted consistently across platforms.