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

compiler/testData/diagnostics/tests/controlFlowAnalysis/kt610.fir.kt

@@ -0,0 +1,10 @@
+//KT-610 Distinguish errors 'unused variable' and 'variable is assigned but never accessed'
+
+package kt610
+
+fun foo() {
+    var j = 9  //'unused variable' error
+
+    var i = 1  //should be an error 'variable i is assigned but never accessed'
+    i = 2
+}