FIR: Fix test data after making LHS of assignment an expression

KT-54648

compiler/testData/diagnostics/tests/generics/varProjection/setterProjectedOutNoPlusAssign.kt

@@ -1,4 +1,3 @@
-// FIR_IDENTICAL
 // !DIAGNOSTICS: -UNREACHABLE_CODE
 interface Tr<T> {
     var v: T
@@ -8,4 +7,4 @@ fun test(t: Tr<out String>) {
     // resolved as t.v = t.v + null!!, where type of right operand is String,
     // so TYPE_MISMATCH: String is not <: of Captured(out String)
     <!SETTER_PROJECTED_OUT!>t.v<!> += null!!
-}
+}