docs: fix broken hyperlink to Tornado #2171

Job	Run time
Check Links	5m 26s
integration_check (ubuntu-latest, 3.8)	58s
integration_check (ubuntu-latest, 3.9)	53s
integration_check (ubuntu-latest, 3.10)	57s
integration_check (ubuntu-latest, 3.11)	1m 3s
build (ubuntu-latest, 3.8)	2m 35s
build (ubuntu-latest, 3.11)	3m 3s
build (windows-latest, 3.8)	11m 58s
build (windows-latest, 3.11)	13m 29s
build (macos-latest, 3.8)	2m 8s
build (macos-latest, 3.11)	2m 6s
build (windows-latest, 3.9)	14m 0s
build (ubuntu-latest, pypy-3.8)	8m 2s
build (macos-latest, 3.10)	2m 4s
build (ubuntu-latest, 3.12)	3m 21s
check_release	2m 36s
integration_check_pypy	1m 29s
Test Docs	1m 26s
Make SDist	46s
Test Examples	1m 2s
Test Lint	1m 47s
Test Minimum Versions	4m 36s
Test Prereleases	3m 58s
Install from SDist and Test	1m 14s
coverage	0s
tests_check	3s
	1h 31m 0s

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