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

compiler/testData/diagnostics/tests/controlFlowAnalysis/deadCode/deadCodeInAssignment.fir.kt

@@ -0,0 +1,18 @@
+fun testAssignment() {
+    var a = 1
+    a = todo()
+}
+
+fun testVariableDeclaration() {
+    val a = todo()
+}
+
+fun testPlusAssign() {
+    operator fun Int.plusAssign(i: Int) {}
+
+    var a = 1
+    a += todo()
+}
+
+
+fun todo(): Nothing = throw Exception()