[ProtocolConformance] Compute the correct un-availability for inherited

conformances.

(cherry picked from commit e2ddc6c)

Author: hborla

lib/AST/ProtocolConformanceRef.cpp

@@ -287,7 +287,8 @@ bool ProtocolConformanceRef::hasUnavailableConformance() const {
 
   // Check whether this conformance is on an unavailable extension.
   auto concrete = getConcrete();
-  auto ext = dyn_cast<ExtensionDecl>(concrete->getDeclContext());
+  auto *dc = concrete->getRootConformance()->getDeclContext();
+  auto ext = dyn_cast<ExtensionDecl>(dc);
   if (ext && AvailableAttr::isUnavailable(ext))
     return true;
 

lib/Sema/TypeCheckConcurrency.cpp

@@ -6464,9 +6464,6 @@ ProtocolConformance *swift::deriveImplicitSendableConformance(
       auto inheritedConformance = classModule->checkConformance(
           classDecl->mapTypeIntoContext(superclass),
           proto, /*allowMissing=*/false);
-      if (inheritedConformance.hasUnavailableConformance())
-        inheritedConformance = ProtocolConformanceRef::forInvalid();
-
       if (inheritedConformance) {
         inheritedConformance = inheritedConformance
             .mapConformanceOutOfContext();