deps: update to libuv v1.26.0

Notable changes since v1.23.2:

- v1.26.0
  - uv_os_uname()
  - unix: don't attempt to invalidate invalid fd
    1ce6393a57
- v1.25.0
  - unix: better handling of unsupported F_FULLFSYNC (fixes #6725)
    6fc797c3fe
  - tty,win: fix Alt+key under WSL
    d2e59bb600
  - fsevents: really watch files with fsevents on macos 10.7+
    2d2af382ce
  - win: fix duplicate tty vt100 fn key
- v1.24.0
  - win,fs: retry if uv_fs_rename fails
    e94c184c7c
    - later [reverted](https://github.com/libuv/libuv/issues/2098) but may be useful reference
  - win: support more fine-grained windows hiding
    4c2dcca27b

src/nvim/os/fs.c

@@ -649,13 +649,6 @@ int os_fsync(int fd)
   int r;
   RUN_UV_FS_FUNC(r, uv_fs_fsync, fd, NULL);
   g_stats.fsync++;
-#ifdef __APPLE__
-  // TODO(justinmk): Remove this after it is fixed in libuv. #6725
-  if (r == UV_ENOTSUP) {
-    int rv = fsync(fd);
-    return rv ? -rv : rv;
-  }
-#endif
   return r;
 }