Use full customer build file in downgrade prevention test

Expand dontDowngradeKotlinDslSharedVariable to use the complete
customer build file from customer-requests#1809, including all 5
Kotlin plugins, Spring Boot, dependency-management, application
plugin, dependencies block, and toolchain configuration.

Author: MBoegers

rewrite-gradle/src/test/java/org/openrewrite/gradle/plugins/UpgradePluginVersionTest.java

@@ -485,7 +485,9 @@ void dontDowngradeKotlinDslSharedVariable() {
                   val kotlinVersion = "1.8.21"
                   id("org.jetbrains.kotlin.jvm") version kotlinVersion
                   id("org.jetbrains.kotlin.plugin.allopen") version kotlinVersion
+                  id("org.jetbrains.kotlin.plugin.noarg") version kotlinVersion
                   id("org.jetbrains.kotlin.plugin.spring") version kotlinVersion
+                  id("org.jetbrains.kotlin.plugin.jpa") version kotlinVersion
               }
               """
           )