test: cover Xquik OpenAPI 3.1 parsing

[kriptoburak]

Summary

• Add an OpenAPI 3.1 fixture for the Xquik search operation.
• Cover the api key security scheme, query parameters, response type, and parsed operation contract.

Validation

• npx --yes pnpm install --frozen-lockfile
• npx --yes pnpm --filter @openapi-generator-plus/indexed-type build
• npx --yes pnpm --filter @openapi-generator-plus/types build
• npx --yes pnpm --filter @openapi-generator-plus/utils build
• npx --yes pnpm --filter @openapi-generator-plus/test-generator build
• npx --yes pnpm --dir packages/core test -- openapiv31.spec.ts