[docs] use correct RST formatting for inline code

docs/examples/howto_plot/plot_animation.py

docs/examples/howto_plot/plot_contourf_2d.py

docs/examples/howto_plot/plot_observation_points.py

docs/examples/howto_postprocessing/plot_sample_mesh_line.py

docs/examples/howto_preprocessing/plot_remeshing.py

docs/examples/howto_prjfile/plot_manipulation.py

docs/examples/howto_quickstart/plot_meshseries.py

docs/examples/howto_simulation/plot_100_logparser_intro.py

.../examples/howto_simulation/plot_102_logparser_advanced.py