Add defusedxml as a dev dependency

See sphinx-doc/sphinx#12339

changelog.d/20240430_155714_jsick_DM_44137.md

@@ -1,3 +1,7 @@
 ### Bug fixes
 
 - Technotes ignore files in the repository with `.md`, `.rst`, and `.ipynb` extensions if they aren't the index file. Since technotes are single-page documents, only the index file should be used as a source file. This change lets authors include auxiliary notebooks with their technotes without having to explicitly exclude them from the technote build process. This is implemented with `technote.conf.extend_excludes_for_non_index_source`.
+
+### Other changes
+
+- Added `defusedxml` as a dev dependency. This is used by Sphinx's `sphinx.testing.fixtures`, but isn't included as a dependency by Sphinx itself. This change ensures that `defusedxml` is installed when running the tests.

pyproject.toml

@@ -47,6 +47,7 @@ dev = [
     # Test depedendencies for analyzing HTML output
     "lxml",
     "cssselect",
+    "defusedxml",  # used by Sphinx but not declared as a dependency
     # Extensions for documenteer's own docs
     "sphinx-click",
     "sphinxcontrib-autoprogram",
@@ -56,6 +57,7 @@ dev = [
     "types-PyYAML",
     "types-docutils",
     "types-mock",
+    # Testing dependencies
 ]
 guide = [
     # Theme and extensions for Rubin user guide projects