test/xi2: Fix mask size in XISelectEvents test

XI2LASTEVENT identifies the bit number, not the mask size in bits. The
mask size in bits is XI2LASTEVENT + 1 and the mask size in bytes is
(XI2LASTEVENT + 8) / 8 or XI2MASKSIZE.
4 jobs for misc-input-cleanups in 5 minutes and 1 second (queued for 2 seconds)
Status Name Job ID Coverage
  Docker Image
passed debian-buster #5794498

00:00:15

 
  Build And Test
passed autotools #5794499

00:04:46

passed meson #5794500

00:01:44

passed meson-noglamor #5794501

00:01:17