correctly convert pd.CategoricalDType #665

Job	Run time
⬢ Prepare Node.js	22s
🐍 Prepare Python	37s
🔍 Check if pull request	5s
🧱 Build test matrix	8s
🔍 Check	2m 16s
🗃 Build datasets	2m 8s
🧱 Build Spotlight	2m 57s
📝 Build API docs	40s
🧪 Doc Test	1m 8s
🧪 Unit Test	1m 29s
🧪 UI Test (chrome)	3m 45s
🧪 UI Test (firefox)	3m 31s
🔍 Check wheel contents	53s
🧪 Integration Test (ubuntu-latest, 3.8)	11m 15s
🚀 Release Spotlight	0s
	31m 14s

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