Drop old Sphinx version constraint to pick up global constraint #1976

Job	Run time
Pytest Conda Py3 POCL	2m 47s
basedpyright	1m 50s
Documentation	2m 4s
Typos	8s
Examples Conda Py3	1m 30s
Ruff	5s
Tests for downstream project mirgecom_examples	6s
Tests for downstream project meshmode	10m 19s
Tests for downstream project grudge	11m 12s
Pytest Conda Py3 Intel	2m 28s
Tests for downstream project mirgecom	5s
	32m 34s

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