[FIR] Prevent replacing UNNECESSARY_SAFE_CALL with UNEXPECTED_SAFE_CALL

UNNECESSARY_SAFE_CALL is a warning,
UNEXPECTED_SAFE_CALL is an error, thus
it's a breaking change.

Also see KT-60695.

^KT-59860 Fixed


Merge-request: KT-MR-11210
Merged-by: Nikolay Lunyak <Nikolay.Lunyak@jetbrains.com>

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

@@ -2,6 +2,6 @@
 
 fun test() {
     val b: Int
-    run { b = 1 }<!UNEXPECTED_SAFE_CALL!>?.<!>let {}
+    run { b = 1 }<!UNNECESSARY_SAFE_CALL!>?.<!>let {}
     b.inc()
 }