2.1.274

Update asciidoctor-pdf requirement from 2.3.13 to 2.3.15 (#385)

Updates the requirements on [asciidoctor-pdf](https://github.com/asciidoctor/asciidoctor-pdf) to permit the latest version.
- [Release notes](https://github.com/asciidoctor/asciidoctor-pdf/releases)
- [Changelog](https://github.com/asciidoctor/asciidoctor-pdf/blob/main/CHANGELOG.adoc)
- [Commits](https://github.com/asciidoctor/asciidoctor-pdf/compare/v2.3.13...v2.3.15)

---
updated-dependencies:
- dependency-name: asciidoctor-pdf
  dependency-type: direct:production
...

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