ci: Add doctests to CI again.

[hameerabbasi]

What type of PR is this? (check all applicable)

• [ ] 💾 Refactor
• [ ] 🪄 Feature
• [ ] 🐞 Bug Fix
• [ ] 🔧 Optimization
• [ ] 📚 Documentation
• [x] 🧪 Test
• [ ] 🛠️ Other

Related issues

• Related issue #
• Closes #

Checklist

• [x] Code follows style guide
• [x] Tests added
• [x] Documented the changes

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Please explain your changes below.

[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #767 will improve performances by ×2.1

_{Comparing hameerabbasi:doctests-2 (91a12fa) with main (7f31435)}

Summary

⚡ 2 improvements ✅ 338 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	hameerabbasi:doctests-2	Change
⚡	test_index_fancy[side=100-rank=1-format='coo']	1,395.6 µs	679.6 µs	×2.1
⚡	test_index_slice[side=100-rank=2-format='gcxs']	2.9 ms	2.4 ms	+23.71%

[hameerabbasi]

@willow-ahrens Doctest issue.