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

compiler/testData/diagnostics/testsWithStdLib/smartcasts/forEachUnsafe.fir.kt

@@ -0,0 +1,14 @@
+// KT-7186: False "Type mismatch" error
+
+fun indexOfMax(a: IntArray): Int? {
+    var maxI: Int? = 0
+    a.forEachIndexed { i, value ->
+        if (value >= a[maxI]) {
+            maxI = i
+        }
+        else if (value < 0) {
+            maxI = null
+        }
+    }
+    return maxI
+}