[BUG] Multiple oauth2 flows cause typescript-node generation syntax errors

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?

Description

When generating SDK code using the generate command, typescript-node implementation has syntax errors in the API code when there are two or more oauth2 flows defined in the securitySchema

openapi-generator version

java -jar openapi-generator-cli.jar version
6.0.1

OpenAPI declaration file content or url

components:
  securitySchemes:
    oauth2:
      type: oauth2
      description: simple authentication
      flows:
        clientCredentials:
          tokenUrl: https://oauth/token
          scopes: 
            all: 'access to all scopes'
        authorizationCode:
          authorizationUrl: https://oauth/authorize
          tokenUrl: https://oauth/token
          scopes: 
            all: 'access to all scopes'

full file can be found here: example-api.yaml

Generation Details

java -jar openapi-generator-cli.jar generate -i example-api.yaml -g typescript-node -o sdk

Steps to reproduce

after generating the source files, you will see the following in the defaultApi.ts:

    protected authentications = {
        'default': <Authentication>new VoidAuth(),
        'oauth2': new OAuth(),
        'oauth2': new OAuth(),
    }

which prevents tsc from being able to build the file.

Related issues/PRs

I have not found a related issue

Use example-api.yaml with the documented typescript-node generation command, then inspect the generated defaultApi.ts. Start by tracing how the two OAuth2 flows become entries in the authentications object. Done means the generated TypeScript no longer contains duplicate oauth2 keys and can build successfully with tsc.