refactor: de-duplicate the split tests

(following the verbatim copy in #418)

- removes the tests that depend on unit-test-input yaml from unit
- removes the tests that don't depend on this from integration

Author: mnahkies

packages/openapi-code-generator/src/test/input.test-utils.ts

@@ -12,7 +12,7 @@ import {OpenapiValidator} from "../core/openapi-validator"
 
 export type OpenApiVersion = "3.0.x" | "3.1.x"
 
-function getTestVersions(): OpenApiVersion[] {
+function getTestVersions(): [OpenApiVersion, ...OpenApiVersion[]] {
   if (process.argv.find((arg) => ["--updateSnapshot", "-u"].includes(arg))) {
     logger.warn("Running with --updateSnapshot - only testing one version")
     return ["3.0.x"]