[3.12] gh-114492: Initialize struct termios before calling tcgetattr() (GH-114495) (GH-114502)

On Alpine Linux it could leave some field non-initialized.
(cherry picked from commit d22c066)

Co-authored-by: Serhiy Storchaka <[email protected]>

Author: miss-islington

Misc/NEWS.d/next/Library/2024-01-23-21-20-40.gh-issue-114492.vKxl5o.rst

@@ -0,0 +1,2 @@
+Make the result of :func:`termios.tcgetattr` reproducible on Alpine Linux.
+Previously it could leave a random garbage in some fields.

Modules/termios.c

@@ -84,6 +84,8 @@ termios_tcgetattr_impl(PyObject *module, int fd)
     struct termios mode;
     int r;
 
+    /* Alpine Linux can leave some fields uninitialized. */
+    memset(&mode, 0, sizeof(mode));
     Py_BEGIN_ALLOW_THREADS
     r = tcgetattr(fd, &mode);
     Py_END_ALLOW_THREADS