[FIR-TEST] Add new testdata generated after changes in previous commit

compiler/testData/diagnostics/tests/reassignment/foronly.fir.kt

@@ -0,0 +1,9 @@
+// !DIAGNOSTICS: -UNUSED_VALUE
+
+fun foo(k: Int): Int {
+    val i: Int
+    for (j in 1..k) {
+        i = j
+    }
+    return i
+}