Aborted attempted copy warning about `redoc.js`

[rra]

Starting with Sphinx 8, use of sphinxcontrib-redoc produces the following warning for any build after the first:

WARNING: Aborted attempted copy from /home/eagle/lsst/gafaelfawr/.tox/docs/lib/python3.12/site-packages/sphinxcontrib/redoc.js to /home/eagle/lsst/gafaelfawr/docs/_build/html/_static/redoc.js (the destination path has existing data). [misc.copy_overwrite]

If the text of the warning is correct, I suspect this means that the already-present copy in the build tree is not updated. I believe there's a new force=True option to the relevant Sphinx utility function that forces the overwrite. Perhaps that should be used here.