Fix DtypeError message for reference validation #936

	name: Check Sphinx links
	on:
	pull_request:
	schedule:
	- cron: '0 5 * * *' # once per day at midnight ET
	workflow_dispatch:

	jobs:
	check-sphinx-links:
	runs-on: ubuntu-latest
	concurrency:
	group: ${{ github.workflow }}-${{ github.ref }}
	cancel-in-progress: true
	steps:
	- name: Checkout repo with submodules
	uses: actions/checkout@v4
	with:
	submodules: 'recursive'
	fetch-depth: 0 # tags are required to determine the version

	- name: Set up Python
	uses: actions/setup-python@v5
	with:
	python-version: '3.11' # TODO update to 3.12 when optional reqs (e.g., oaklib) support 3.12

	- name: Install Sphinx dependencies and package
	run: \|
	python -m pip install --upgrade pip
	python -m pip install -r requirements-doc.txt -r requirements-opt.txt
	python -m pip install .

	- name: Check Sphinx internal and external links
	run: sphinx-build -W -b linkcheck ./docs/source ./test_build

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