Update conf.py to execute imports during pdf building
closes #38451

According [https://ipython.readthedocs.io/en/stable/sphinxext.html](), it should be `ipython_execlines` not `ipython_exec_lines`. Should close issue #38451


hmm so it is. cc @simonjayhawkins  @simonjayhawkins how's this looking will merge this to close #38451 as it does prevent the NameError.

However, something else is awry since `{{ header }}` still appears in the pdf docs.

During the first run of `./make.py latex_forced` it appears in 10 minutes to pandas and no contents are created. we run a second time (I assume to get the contents to build) and on the second run the visualisaztion section is recreated (why this happens is they key to solving this properly) but without the header code being run but the change here means that we don't get the NameErrors Thanks @gepcel  > However, something else is awry since {{ header }} still appears in the pdf docs.

That might because the section (reference) name is "visualization" and the section title is also "visualization", therefore the `Duplicate implicit target name: "visualization"`.