doc: correct parameter type on 'subprocess.kill([signal])'

PR-URL: https://github.com/nodejs/node/pull/27760
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

doc/api/child_process.md

@@ -1022,7 +1022,7 @@ within the child process to close the IPC channel as well.
 added: v0.1.90
 -->
 
-* `signal` {string}
+* `signal` {number|string}
 
 The `subprocess.kill()` method sends a signal to the child process. If no
 argument is given, the process will be sent the `'SIGTERM'` signal. See