night-light: Add a frame around Schedule section for accessibility

This way the Schedule label is correctly read as a header
for the section by screen readers
11 jobs for <span class="ref-name">night-light-a11y</span> in 3 minutes and 32 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #182158
build

00:01:22

 
  Test
passed #182160
asan

00:02:09

passed #182159
test

00:00:46

 
  Manual
manual #182165
allowed to fail manual
armv8
manual #182161
allowed to fail manual
flatpak
manual #182164
allowed to fail manual
msan
manual #182166
allowed to fail manual
ppc64le
manual #182162
allowed to fail manual
tsan
manual #182163
allowed to fail manual
ubsan
 
  Review
manual #182167
allowed to fail manual
review
manual #182168
allowed to fail manual
stop_review