[Clang] Fix a variable shadowing in MapLattice (NFC) (#95697)

Reported in https://pvs-studio.com/en/blog/posts/cpp/1126/, fragment
N10.

The PVS-Studio warning:
V570 The 'C' variable is assigned to itself. MapLattice.h:52

clang/include/clang/Analysis/FlowSensitive/MapLattice.h

@@ -49,7 +49,7 @@ template <typename Key, typename ElementLattice> class MapLattice {
 
   MapLattice() = default;
 
-  explicit MapLattice(Container C) { C = std::move(C); }
+  explicit MapLattice(Container C) : C{std::move(C)} {};
 
   // The `bottom` element is the empty map.
   static MapLattice bottom() { return MapLattice(); }