datetime: Use accessible-description instead of -name for Hour & Minute

In my testing, default orca didn't seem to read the "Hour" or "Minute"
words when we used accessible-name but it does work with
accessible-description.

This is the only place we used accessible-name in gnome-control-center
but we use accessible-description in a few other places.
11 jobs for <span class="ref-name">datetime-a11y</span> in 2 minutes and 56 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #180484
build

00:01:23

 
  Test
passed #180486
asan

00:01:33

passed #180485
test

00:01:17

 
  Manual
manual #180491
allowed to fail manual
armv8
manual #180487
allowed to fail manual
flatpak
manual #180490
allowed to fail manual
msan
manual #180492
allowed to fail manual
ppc64le
manual #180488
allowed to fail manual
tsan
manual #180489
allowed to fail manual
ubsan
 
  Review
manual #180493
allowed to fail manual
review
manual #180494
allowed to fail manual
stop_review