Run docs workflow inside virtualenv to pick up sphinx-build

Author: martinburchell

.github/scripts/build_docs.sh

@@ -26,7 +26,10 @@ git update-index --refresh
 git diff-index --quiet HEAD --
 test -z "$(git ls-files --exclude-standard --others)"
 echo Rebuilding docs
-${PYTHON} "${DOCS_DIR}/rebuild_docs.py" --warnings_as_errors
+
+# Have to be in the virtualenv for sphinx-build to be picked up.
+source "${VENV_DIR}"/bin/activate
+python "${DOCS_DIR}/rebuild_docs.py" --warnings_as_errors
 echo Checking if files generated by rebuild_docs need to be checked in
 git diff
 git update-index --refresh

docs/rebuild_docs.py

@@ -59,8 +59,6 @@
     if args.warnings_as_errors:
         cmdargs.append('SPHINXOPTS="-W"')
 
-    sphinx_build = shutil.which("sphinx-build")
-    cmdargs.append(f"SPHINXBUILD={sphinx_build}")
     subprocess.check_call(cmdargs)
 
     # Copy