Ensure reproducibility of vignettes

[gowerc]

It looks like the advanced vignette slightly changes on every rerun (see diff below) would be good to fix it so that it only changes if the actual code is updated...

<span id="cb9-20"><a href="#cb9-20" aria-hidden="true" tabindex="-1"></a><span class="co">#&gt; &lt;bytecode: 0x7fa8bb8604a8&gt;</span></span>
<span id="cb9-20"><a href="#cb9-20" aria-hidden="true" tabindex="-1"></a><span class="co">#&gt; &lt;bytecode: 0x7f9546ca2148&gt;</span></span>

EDIT:

May also be worth augmenting the cicd job to build the vignettes to also re-commit the files back to the repo (i.e. so they are auto built via cicd)