[BUG][KOTLIN] Fails to compile after updating to 7.25.0 with useJackson3=false useSpringBoot4=true

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator?
• 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

7.25.0 breaks backward compatibility, by force-setting useJackson3=true for Spring 4 and jvm-spring-restclient

It's incorrect to enforce Jackson 3 with those settings: Spring 4.0 and 4.1 work with Jackson 2, it's just deprecated. RestClient still works with Jackson 2.

openapi-generator version

7.25.0, it's a regression compared to 7.24.0

OpenAPI declaration file content or url

Generation Details

See 'steps to reproduce'

Steps to reproduce

I only generate sources and use my own build.gradle.kts, throwing away generator's one.

dependencies {
    api(platform("org.springframework.boot:spring-boot-dependencies:4.0.8"))

    api("org.springframework:spring-web")

    // api because Serializer.jacksonObjectMapper is public
    api("com.fasterxml.jackson.core:jackson-databind")
    api("org.openapitools:jackson-databind-nullable:0.2.11")
    implementation("com.fasterxml.jackson.module:jackson-module-kotlin")
}

openApiGenerate {
    configOptions.set(
        mapOf(
            "omitGradleWrapper" to "true",
            "library" to "jvm-spring-restclient",
            "useSpringBoot3" to "true",
            "useSpringBoot4" to "true",
            "useJackson3" to "false",
            "serializationLibrary" to "jackson",
        )
    )
}

What complied with 7.24.0, fails to compile in 7.25.0 because Serializer.kt is now:

import tools.jackson.databind.DeserializationFeature
import tools.jackson.databind.json.JsonMapper
import tools.jackson.databind.cfg.DateTimeFeature
import com.fasterxml.jackson.annotation.JsonInclude
import tools.jackson.module.kotlin.jsonMapper
import tools.jackson.module.kotlin.kotlinModule

object Serializer {
    @JvmStatic
    val jacksonObjectMapper: JsonMapper = jsonMapper {
        addModule(kotlinModule())
        changeDefaultPropertyInclusion { it.withValueInclusion(JsonInclude.Include.NON_ABSENT) }
        disable(DateTimeFeature.WRITE_DATES_AS_TIMESTAMPS)
        disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES)
    }
}

Because I explicitly set useJackson3=false, the generated code should import com.fasterxml.jackson

Related issues/PRs

#24709

Suggest a fix

Remove the addition of setUseJackson3(true) as pointed out in https://github.com/OpenAPITools/openapi-generator/pull/24709/changes#r3917417022

Start with the generated Serializer.kt shown in the report and compare generation with 7.24.0 versus 7.25.0 using the provided Gradle options. Read the change and discussion in related issue or PR #24709, then verify that useJackson3=false produces com.fasterxml.jackson imports and that the generated sources compile with Spring Boot 4 and Jackson 2.