Replace deprecated g_string_sprintf by g_string_printf
Fixes warnings as:
| ../git/sysex.c: In function 'decode_sysex':
| ../git/sysex.c:88:13: warning: g_string_printf
| 88 | g_string_sprintf(
| | ^~~~~~~~~
| ../git/sysex.c:117:13: warning: g_string_printf
| 117 | g_string_sprintf(
| | ^~~~~~~~~
| ../git/sysex.c:167:13: warning: g_string_printf
| 167 | g_string_sprintf(
| | ^~~~~~~~~
Signed-off-by: Andreas Müller <schnitzeltony@gmail.com>
(cherry picked from commit
6e0376e199323a7319617b027841fe78b97b1a34)