yambar: disable blanket -Werror, fix gcc-13 build

Without the change `yambar` fails to build on `gcc-13` as:

    yambar> ../plugin.c: In function 'plugin_load':
    yambar> ../plugin.c:279:35: warning: '%s' directive argument is null [-Wformat-truncation=]
    yambar>   279 |     snprintf(path, sizeof(path), "%s_%s.so", type2str(type), name);
    yambar>       |                                   ^~

Co-authored-by: Anderson Torres <torres.anderson.85@protonmail.com>

pkgs/applications/misc/yambar/default.nix

@@ -82,6 +82,7 @@ stdenv.mkDerivation (finalAttrs: {
   mesonBuildType = "release";
 
   mesonFlags = [
+    (lib.mesonBool "werror" false)
     (lib.mesonEnable "backend-x11" x11Support)
     (lib.mesonEnable "backend-wayland" waylandSupport)
   ];