docs: Ignore a venv generated during docs build.

To build some of the docs dynamically, a new virtualenv is created.
Without this ignore, sphinx also reads all the files under that tree and
then complains that they're not properly linked to the rest of the docs.

docs/conf.py

@@ -126,7 +126,13 @@ language = 'en'
 # List of patterns, relative to source directory, that match files and
 # directories to ignore when looking for source files.
 # This pattern also affects html_static_path and html_extra_path.
-exclude_patterns = ['_build', 'Thumbs.db', '.DS_Store']
+exclude_patterns = [
+    "_build",
+    "Thumbs.db",
+    ".DS_Store",
+    ".venv",
+    "references/docs/.venv",
+]
 
 # The name of the Pygments (syntax highlighting) style to use.
 pygments_style = None
@@ -369,6 +375,7 @@ def on_init(app):  # lint-amnesty, pylint: disable=redefined-outer-name, unused-
                     exclude.append(os.path.join(dirpath, name))
         if exclude:
             args.extend(exclude)
+
         check_call(args)