Fix our deduction guide

Author: gennaroprota

include/boost/static_string/static_string.hpp

@@ -6529,7 +6529,7 @@ to_static_wstring(long double value) noexcept
 #ifdef BOOST_STATIC_STRING_USE_DEDUCT
 template<std::size_t N, typename CharT>
 basic_static_string(const CharT(&)[N]) ->
-  basic_static_string<N, CharT, std::char_traits<CharT>>;
+  basic_static_string<N - 1, CharT, std::char_traits<CharT>>;
 #endif
 
 //------------------------------------------------------------------------------

test/constexpr_tests.hpp

@@ -110,6 +110,7 @@ testConstantEvaluation()
   // Check construction in a constexpr context
   constexpr basic_static_string s("hello");
   static_assert(s.size() == 5);
+  static_assert(s.static_capacity == 5);
   static_assert(s == "hello");
 
   // Check assignment in a constexpr context