fix comment reference from man 7 signal to man 7 signal-safety (#138554)

docs: fix comment reference from man 7 signal to man 7 signal-safety

Modules/_posixsubprocess.c

@@ -630,7 +630,7 @@ reset_signal_handlers(const sigset_t *child_sigmask)
  * (v)fork to set things up and call exec().
  *
  * All of the code in this function must only use async-signal-safe functions,
- * listed at `man 7 signal` or
+ * listed at `man 7 signal-safety` or
  * http://www.opengroup.org/onlinepubs/009695399/functions/xsh_chap02_04.html.
  *
  * This restriction is documented at

Modules/signalmodule.c

@@ -1943,7 +1943,7 @@ signal_install_handlers(void)
 /* Restore signals that the interpreter has called SIG_IGN on to SIG_DFL.
  *
  * All of the code in this function must only use async-signal-safe functions,
- * listed at `man 7 signal` or
+ * listed at `man 7 signal-safety` or
  * http://www.opengroup.org/onlinepubs/009695399/functions/xsh_chap02_04.html.
  *
  * If this function is updated, update also _posix_spawn() of subprocess.py.

Python/pylifecycle.c

@@ -3595,7 +3595,7 @@ PyOS_getsig(int sig)
 
 /*
  * All of the code in this function must only use async-signal-safe functions,
- * listed at `man 7 signal` or
+ * listed at `man 7 signal-safety` or
  * http://www.opengroup.org/onlinepubs/009695399/functions/xsh_chap02_04.html.
  */
 PyOS_sighandler_t