FIR: fix suspend type serialization

compiler/testData/codegen/box/fir/SuspendExtension.kt

@@ -0,0 +1,19 @@
+// TARGET_BACKEND: JVM
+// IGNORE_BACKEND: JVM
+// MODULE: lib
+// FILE: A.kt
+
+class CoroutineScope
+
+suspend fun <T> runWithTimeout(
+    block: suspend CoroutineScope.() -> T
+): T? = null
+
+// MODULE: main(lib)
+// FILE: B.kt
+
+suspend fun foo(): Boolean = runWithTimeout {
+    false
+} ?: true
+
+fun box(): String = "OK"