[BUG][JAVA] Not compilable code generated when oneOf refs to an array type

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

When oneOf refs to an array type, then the generated code is not compilable. java.util.List isn't imported and other compile time errors emerge.

openapi-generator version

6.0.1 maven plugin. I don't know if it's a regression as I've never had same situation with previous versions.

OpenAPI declaration file content or url

oneOf:
 - type: string
 - $ref: '#/components/schemas/my_array'
my_array:
 type: array
 items: {}

Generation Details

      <plugin>
        <groupId>org.openapitools</groupId>
        <artifactId>openapi-generator-maven-plugin</artifactId>
        <version>${openapi-generator.version}</version>
        <executions>
          <execution>
            <goals>
              <goal>generate</goal>
            </goals>
            <configuration>
              <inputSpec>${project.basedir}/src/main/resources/my-api.yaml</inputSpec>
              <generatorName>java</generatorName>
              <configOptions>
                <sourceFolder>src/gen/java/main</sourceFolder>
                <library>native</library>
                <dateLibrary>java8</dateLibrary>
                <serializationLibrary>jackson</serializationLibrary>
              </configOptions>
            </configuration>
          </execution>
        </executions>
      </plugin>

Steps to reproduce

mvn compile

Related issues/PRs

https://github.com/OpenAPITools/openapi-generator/issues/8765
https://github.com/OpenAPITools/openapi-generator/issues/6015
https://github.com/OpenAPITools/openapi-generator/issues/5997

Suggest a fix

The generated code semantically is fine in human POV. Likely a bit change in compiler will make it syntactically fine too.

Start with the supplied OpenAPI YAML and the openapi-generator-maven-plugin configuration using generatorName java; run mvn compile to reproduce the generated-code failure. Compare the generated Java for the oneOf array reference with the expected imports and compilation errors, then verify that the generated client compiles successfully.