Fix warning in doc generation

12 jobs for doc_fixups in 13 minutes and 21 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build Docker
passed #1107162
build_docker_from_cache

00:00:17

 
  Test
passed #1107164
test_mpi

00:00:19

passed #1107163
test_serial

00:05:14

86.0%
 
  Demo Runs
passed #1107171
run_bernoulli

00:00:31

passed #1107172
run_curve_fitting

00:00:29

passed #1107167
run_getting_started_1

00:00:34

passed #1107168
run_getting_started_2

00:01:00

passed #1107169
run_getting_started_3

00:02:05

passed #1107170
run_getting_started_mf

00:07:48

passed #1107165
run_ipynb0

00:01:36

passed #1107166
run_ipynb1

00:00:43

passed #1107173
run_visual_mgvi

00:01:23