Deduplicate incompatible actual descriptors

Otherwise, we might get false positive AMBIGUOUS_ACTUALS due to one and
the same descriptor appearing multiple times in a list

compiler/frontend/src/org/jetbrains/kotlin/resolve/checkers/ExpectedActualDeclarationChecker.kt

@@ -138,7 +138,12 @@ class ExpectedActualDeclarationChecker(
             }
 
         // Several compatible actuals on one path: report AMBIGUIOUS_ACTUALS here
-        val atLeastWeaklyCompatibleActuals = compatibility.filterKeys { it.isCompatibleOrWeakCompatible() }.values.flatten()
+        val atLeastWeaklyCompatibleActuals = compatibility
+            .filterKeys { it.isCompatibleOrWeakCompatible() }
+            .values
+            .flatten()
+            .distinct()
+
         if (atLeastWeaklyCompatibleActuals.size > 1) {
             trace.report(Errors.AMBIGUOUS_ACTUALS.on(
                 reportOn,

idea/testData/multiModuleHighlighting/hierarchicalExpectActualMatching/weaklyIncompatibleActualInIntermediateModule/top/top.kt

@@ -1,5 +1,5 @@
 package sample
 
-expect class <!AMBIGUOUS_ACTUALS("Class 'A'", "middle, middle")!>A<!> {
+expect class A {
     fun f()
 }