bump test env from debian 12 to debian 13

bump test env from debian 12 to debian 13

debian 13 comes with a newer version of xterm which has some changes
in `print-immediate`. this requires us to update test fixtures. the
changes are:

          test_64bit: invisible was previously emitted as spaces.
                      now emitted with escape codes.

     test_color_true: 0x808080 was previously emitted as
                      128:128:120. now emitted as 128:128:128.

            test_egc: fullwidth char with combining characters was
                      previously emitted with U+FFFF (invalid) in the
                      2nd cell, now emitted without.

   test_invalid_utf8: U+FFFD (replacement char) is now emitted as
                      a hash char ("#").

  test_non_printable: ditto

          test_print: ditto

also bump php from 8.3 to 8.4.