Add a testcase for the -Wdangling-assignment-gsl warning, NFC.

Author: hokein

clang/test/Sema/warn-lifetime-analysis-nocfg.cpp

@@ -713,7 +713,7 @@ struct [[gsl::Pointer]] Span {
 // Pointer from Owner<Pointer>
 std::string_view test5() {
   std::string_view a = StatusOr<std::string_view>().valueLB(); // expected-warning {{object backing the pointer will be dest}}
-return StatusOr<std::string_view>().valueLB(); // expected-warning {{returning address of local temporary}}
+  return StatusOr<std::string_view>().valueLB(); // expected-warning {{returning address of local temporary}}
 
   // No dangling diagnostics on non-lifetimebound methods.
   std::string_view b = StatusOr<std::string_view>().valueNoLB();
@@ -724,6 +724,7 @@ return StatusOr<std::string_view>().valueLB(); // expected-warning {{returning a
 // Prevent regression GH108463
 Span<int*> test6(std::vector<int*> v) {
   Span<int *> dangling = std::vector<int*>(); // expected-warning {{object backing the pointer}}
+  dangling = std::vector<int*>(); // expected-warning {{object backing the pointer}}
   return v; // expected-warning {{address of stack memory}}
 }