Replace obsolete function point-at-eol with equivalent.

Emacs 29.1+ emits a warning when code using `point-at-eol` is compiled; see
emacs/master commit b7e867. This is a trivial but safe change to get rid of that
warning. `point-at-eol` seems to have been the same thing as `line-end-position`
since 1999 (emacs/master commit 475fb2f). I've tested this briefly and the
behavior of `zig-end-of-defun` does seem to be the same with this change.

Author: dpathakj

zig-mode.el

@@ -321,7 +321,7 @@ This is written mainly to be used as `end-of-defun-function' for Zig."
   (interactive)
 
   ;; Jump over the function parameters and paren-wrapped return, if they exist.
-  (while (re-search-forward "(" (point-at-eol) t)
+  (while (re-search-forward "(" (line-end-position) t)
     (progn
       (backward-char)
       (forward-sexp)))