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

compiler/testData/diagnostics/tests/operatorsOverloading/AssignOperatorAmbiguity.fir.kt

@@ -0,0 +1,17 @@
+//KT-1820 Write test for ASSIGN_OPERATOR_AMBIGUITY
+package kt1820
+
+class MyInt(val i: Int) {
+    operator fun plus(m: MyInt) : MyInt = MyInt(m.i + i)
+}
+
+operator fun Any.plusAssign(a: Any) {}
+
+fun test(m: MyInt) {
+    m += m
+
+    var i = 1
+    <!ASSIGN_OPERATOR_AMBIGUITY!>i += 34<!>
+}
+
+