pdf: update year to 2026 in copyright.tex (#3042) #8177

Job	Run time
check-file-encoding	10s
check-git-conflicts	10s
markdownlint	24s
check-unclosed-tags	11s
verify-internal-link-anchors	21s
verify-internal-links	1m 43s
check-control-characters	10s
check-manual-line-breaks	10s
	3m 19s

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