_rencode.pyx: fix build warnings

[pkubaj]

[1/1] Cythonizing rencode/_rencode.pyx
rencode/_rencode.c:2927:28: warning: result of comparison of constant 128 with expression of type 'signed char' is always true [-Wtautological-constant-out-of-range-compare]
 2927 |     __pyx_t_1 = (__pyx_v_x < 0x80);
      |                  ~~~~~~~~~ ^ ~~~~
rencode/_rencode.c:7905:35: warning: result of comparison of constant 256 with expression of type 'unsigned char' is always true [-Wtautological-constant-out-of-range-compare]
 7905 |     __pyx_t_1 = (__pyx_v_typecode < (__pyx_e_7rencode_8_rencode_LIST_FIXED_START + __pyx_e_7rencode_8_rencode_LIST_FIXED_COUNT));
      |                  ~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2 warnings generated.