chore: fix malformed f-string (#2563)

* fix: incorrect f-string in docling.datamodel.document

* DCO Remediation Commit for Johannes Damp <jdamp@users.noreply.github.com>

I, Johannes Damp <jdamp@users.noreply.github.com>, hereby add my Signed-off-by to this commit: 0f690a863a2fccc8f8c110e3b2a57a1f9f25e641

Signed-off-by: Johannes Damp <jdamp@users.noreply.github.com>

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Signed-off-by: Johannes Damp <jdamp@users.noreply.github.com>