FIR: Temporary adjust diagnostic tests

Elvis now is being resolved a bit differently and in case
of inconsistent types, the while expression has error type,
but no diagnostic is reported since the element has no valid source element

When one sets the source
https://github.com/JetBrains/kotlin/commit/817316cdc93457c1de7cf10c3b422e3a4b486e5b
it brings back the issue KT-45989 that was effectively unresolved but hidden
due to diagnostic loss

^KT-45989 Open

compiler/testData/diagnostics/tests/typeParameters/implicitNothingInReturnPosition.fir.kt

@@ -39,7 +39,7 @@ class Context<T>
 fun <T> Any.decodeIn(typeFrom: Context<in T>): T = something()
 
 fun <T> Any?.decodeOut1(typeFrom: Context<out T>): T {
-    return <!RETURN_TYPE_MISMATCH!>this?.decodeIn(typeFrom) ?: kotlin.Unit<!>
+    return this?.decodeIn(typeFrom) ?: kotlin.Unit
 }
 
 fun <T> Any.decodeOut2(typeFrom: Context<out T>): T {

compiler/testData/diagnostics/tests/when/kt9972.fir.kt

@@ -20,9 +20,9 @@ fun test1(): Int {
 }
 
 fun test2(): Int {
-    val x: String = <!INITIALIZER_TYPE_MISMATCH!>when {
+    val x: String = when {
                         true -> Any()
                         else -> null
-                    } ?: return 0<!>
+                    } ?: return 0
     return x.hashCode()
 }