TOOLSDEV-545: Fix display of hat symbols over variables

[theresa-jones]

This adds the attribute accent="true" to ^ elements in configurations. E.g. so that \hat{A} will convert to A^ rather than to the current output. A^.

Display-wise this has the effect of flattening out the (currently too tall) variable hats.

[nadamsoreilly]

@theresa-jones I see that the CI is failing on the Python 3.9. I am guessing that there is some issue with Poetry in Python 3.9. I don't think it's important that we test 3.9 anymore. I'm going to push up another commit to this branch that removes that check.

[theresa-jones]

Back to non-draft status! I had marked it a draft because the tests didn't pass, but they do in fact pass for me when I run them locally. There seems to be a pre-existing problem with the tests on staging, not related to this minor update. (Looking at past PRs, the test do pass on production though)