Cache documentation files for faster CI

5 jobs for docu-speedup in 54 seconds (queued for 1 second)
Status Name Job ID Coverage
  Prepare
passed docker #1230569
shell linux

00:00:08

 
  Test
passed test:export-against-exported-files #1230572
docker

00:00:13

passed test:export-against-imported-files #1230571
docker

00:00:13

passed test:import #1230570
docker

00:00:13

 
  Generate
passed documentation #1230573
docker

00:00:31