[FIR] Fix lower bound of flexible type variable not becoming DNN in warning-severity case

The bug was introduced as part of the implementation for Java
nullability warnings.

#KT-58933 Fixed

compiler/testData/diagnostics/foreignAnnotationsTests/java8Tests/jspecifyOld/warnMode/UnannotatedWildcard.fir.kt

@@ -1,16 +0,0 @@
-// JSPECIFY_STATE: warn
-// FILE: J1.java
-import org.jspecify.nullness.*;
-
-@NullMarked
-public interface J1<T extends @Nullable Object> {
-    T foo();
-}
-
-// FILE: J2.java
-public interface J2 {
-    J1<?> bar();
-}
-
-// FILE: main.kt
-fun baz(j2: J2): Any = <!NULLABILITY_MISMATCH_BASED_ON_JAVA_ANNOTATIONS!>j2.bar().foo()<!> // Any..Any?

compiler/testData/diagnostics/foreignAnnotationsTests/java8Tests/jspecifyOld/warnMode/UnannotatedWildcard.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // JSPECIFY_STATE: warn
 // FILE: J1.java
 import org.jspecify.nullness.*;