CI build failure

[Bruno Haible via Bug reports for the GNU Texinfo documentation system]

The CI today reports a compilation error on Alma Linux 10, NetBSD 11,
and Cygwin 3.3.6:

../../../tta/C/convert/convert_to_info.c: In function 'info_output':
../../../tta/C/convert/convert_to_info.c:752:44: error: \x used with no 
following hex digits
  752 |       text_append_n (&tag_text, "\x{7F}0\n", 3);
      |                                            ^

The correct way to write this string, in C, is
   "\x7F" "0\n"
or
   "\1770\n"

Bruno