namespace: change NameSpace → Namespace

We generally use the casing "Namespace" for the word, and that's visible
in a number of user-facing interfaces, including "RestrictNamespace=" or
"JoinsNamespaceOf=". Let's make sure to use the same casing internally
too.

As discussed in #7024

src/core/execute.c

@@ -2270,7 +2270,7 @@ static int apply_mount_namespace(
         _cleanup_strv_free_ char **rw = NULL, **empty_directories = NULL;
         char *tmp = NULL, *var = NULL;
         const char *root_dir = NULL, *root_image = NULL;
-        NameSpaceInfo ns_info = {
+        NamespaceInfo ns_info = {
                 .ignore_protect_paths = false,
                 .private_dev = context->private_devices,
                 .protect_control_groups = context->protect_control_groups,