Fix plugin test to work with Kotlin 2.1.20

Author: smowton

java/ql/integration-tests/kotlin/linux/custom_plugin/plugin/Plugin.kt

@@ -24,6 +24,7 @@ import org.jetbrains.kotlin.ir.declarations.impl.IrExternalPackageFragmentImpl
 import org.jetbrains.kotlin.ir.declarations.impl.IrFactoryImpl
 import org.jetbrains.kotlin.ir.expressions.IrExpression
 import org.jetbrains.kotlin.ir.expressions.impl.IrCallImpl
+import org.jetbrains.kotlin.ir.expressions.impl.fromSymbolOwner
 import org.jetbrains.kotlin.ir.expressions.impl.IrConstImpl
 import org.jetbrains.kotlin.ir.expressions.impl.IrConstructorCallImpl
 import org.jetbrains.kotlin.ir.symbols.IrClassSymbol