handle TIOCGWINSZ struct correctly

`TIOCGWINSZ` contains 4, not 2 unsigned shorts:
```C
       struct winsize {
           unsigned short ws_row;
           unsigned short ws_col;
           unsigned short ws_xpixel;  /* unused */
           unsigned short ws_ypixel;  /* unused */
       };
```

Fixes the following test failures when building with Python3.14:
```
=========================== short test summary info ============================
FAILED tests/runners.py::Local_::pty::when_pty_True_we_use_pty_fork_and_os_exec - SystemError: buffer overflow
FAILED tests/runners.py::Local_::pty::pty_uses_WEXITSTATUS_if_WIFEXITED - SystemError: buffer overflow
FAILED tests/runners.py::Local_::pty::pty_uses_WTERMSIG_if_WIFSIGNALED - SystemError: buffer overflow
FAILED tests/runners.py::Local_::pty::WTERMSIG_result_turned_negative_to_match_subprocess - SystemError: buffer overflow
FAILED tests/runners.py::Local_::pty::pty_is_set_to_controlling_terminal_size - SystemError: buffer overflow
FAILED tests/runners.py::Local_::pty::spurious_OSErrors_handled_gracefully - SystemError: buffer overflow
FAILED tests/runners.py::Local_::pty::other_spurious_OSErrors_handled_gracefully - SystemError: buffer overflow
FAILED tests/runners.py::Local_::pty::non_spurious_OSErrors_bubble_up - SystemError: buffer overflow
FAILED tests/runners.py::Local_::pty::stop_mutes_errors_on_pty_close - SystemError: buffer overflow
FAILED tests/runners.py::Local_::pty::fallback::can_be_overridden_by_kwarg - SystemError: buffer overflow
FAILED tests/runners.py::Local_::pty::fallback::can_be_overridden_by_config - SystemError: buffer overflow
FAILED tests/runners.py::Local_::pty::fallback::overridden_fallback_affects_result_pty_value - SystemError: buffer overflow
FAILED tests/runners.py::Local_::shell::defaults_to_bash_or_cmdexe_when_pty_True - SystemError: buffer overflow
FAILED tests/runners.py::Local_::shell::may_be_overridden_when_pty_True - SystemError: buffer overflow
FAILED tests/runners.py::Local_::env::uses_execve_for_pty_True - SystemError: buffer overflow
FAILED tests/terminals.py::terminals::pty_size::calls_fcntl_with_TIOCGWINSZ - SystemError: buffer overflow
================== 16 failed, 952 passed, 11 skipped in 6.67s ==================
```

Resolves #1038 .

Author: rathann

invoke/terminals.py

@@ -87,17 +87,18 @@ def _pty_size() -> Tuple[Optional[int], Optional[int]]:
         # Sentinel values to be replaced w/ defaults by caller
         size = (None, None)
         # We want two short unsigned integers (rows, cols)
-        fmt = "HH"
+        # Note: TIOCGWINSZ struct contains 4 unsigned shorts, 2 unused
+        fmt = "HHHH"
         # Create an empty (zeroed) buffer for ioctl to map onto. Yay for C!
-        buf = struct.pack(fmt, 0, 0)
+        buf = struct.pack(fmt, 0, 0, 0, 0)
         # Call TIOCGWINSZ to get window size of stdout, returns our filled
         # buffer
         try:
             result = fcntl.ioctl(sys.stdout, termios.TIOCGWINSZ, buf)
             # Unpack buffer back into Python data types
             # NOTE: this unpack gives us rows x cols, but we return the
             # inverse.
-            rows, cols = struct.unpack(fmt, result)
+            rows, cols, *_ = struct.unpack(fmt, result)
             return (cols, rows)
         # Fallback to emptyish return value in various failure cases:
         # * sys.stdout being monkeypatched, such as in testing, and lacking