Fix PDF build for Python 3.14 #790

Job	Run time
sync / sync	1m 8s
check / Check for zero-width space characters	5s
check / Lint translations	38s
check / Build docs (html)	7m 17s
check / Build docs (epub)	8m 57s
check / Build docs (latex)	7m 12s
check / Build docs (pdf)	10m 43s
	36m 0s

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