fix shadowed variable in string_view.hpp

[alsora]

Signed-off-by: Alberto Soragna alberto.soragna@gmail.com

Building with Wshadow enabled shows this as a shadowed variable error.
Definitely a nitpick in the current code, but still worth fixing.

/workspaces/ros2_galactic/install/behaviortree_cpp_v3/include/behaviortree_cpp_v3/utils/string_view.hpp:880:66: error: declaration of ‘v’ shadows a member of ‘nonstd::sv_lite::basic_string_view<CharT, Traits>::not_in_view’ [-Werror=shadow]
  880 |       nssv_constexpr explicit not_in_view( basic_string_view v ) : v( v ) {}
      |                                                                  ^
/workspaces/ros2_galactic/install/behaviortree_cpp_v3/include/behaviortree_cpp_v3/utils/string_view.hpp:878:31: note: shadowed declaration is here
  878 |       const basic_string_view v;
      |                               ^

[facontidavide]

thanks