tool_getpass: replace getch() call with _getch() on Windows

`getch()` is deprecated according to MSDN:
https://learn.microsoft.com/cpp/c-runtime-library/reference/getch
"The Microsoft-specific function name `getch` is a deprecated alias
for the `_getch` function."

Ref: https://learn.microsoft.com/cpp/c-runtime-library/reference/getch-getwch

Follow-up to 72edb22b8a #15638
Closes #15642

src/tool_getpass.c

@@ -102,7 +102,7 @@ char *getpass_r(const char *prompt, char *buffer, size_t buflen)
   fputs(prompt, tool_stderr);
 
   for(i = 0; i < buflen; i++) {
-    buffer[i] = (char)getch();
+    buffer[i] = (char)_getch();
     if(buffer[i] == '\r' || buffer[i] == '\n') {
       buffer[i] = '\0';
       break;