Update include/asioexec/completion_token.hpp

Fix deprecated header path in warning message

Co-authored-by: Eric Niebler <eniebler@boost.org>

Author: keeAzlynth

include/asioexec/completion_token.hpp

@@ -25,7 +25,7 @@
     "WARNING: The header <asioexec/completion_token.hpp> is deprecated. Please include <exec/asio/completion_token.hpp> instead.")
 #else
 #  warning                                                                                         \
-    "The header <asioexec/asio/completion_token.hpp> is deprecated. Please include <exec/asio/completion_token.hpp> instead."
+    "The header <asioexec/completion_token.hpp> is deprecated. Please include <exec/asio/completion_token.hpp> instead."
 #endif
 
 #include "../exec/asio/completion_token.hpp"  // IWYU pragma: export