Don't skip constraints from equations with the kind equal

The problem was that we didn't incorporate T == Foo into K <: Inv<out T>.
 It happened because of optimisation that isn't applicable here as we
 already have projection in the initial type

 #KT-39777 Fixed

compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/inference/components/ConstraintIncorporator.kt

@@ -221,9 +221,10 @@ class ConstraintIncorporator(
         val isFromVariableFixation = baseConstraint.position.from is FixVariableConstraintPosition
                 || otherConstraint.position.from is FixVariableConstraintPosition
 
-        if (!containsConstrainingTypeWithoutProjection(newConstraint, otherConstraint)
-            && !isUsefulForNullabilityConstraint
-            && !isFromVariableFixation
+        if (!otherConstraint.kind.isEqual() &&
+            !isUsefulForNullabilityConstraint &&
+            !isFromVariableFixation &&
+            !containsConstrainingTypeWithoutProjection(newConstraint, otherConstraint)
         ) return
 
         if (trivialConstraintTypeInferenceOracle.isGeneratedConstraintTrivial(