Bump Asciidoctor-PDF version to 2.3.9

[asciidoctor-updateclibot]

Bump Asciidoctor-PDF version

Update the key ASCIIDOCTOR_PDF_VERSION in the test harness

Updated to content "ASCIIDOCTOR_PDF_VERSION=2.3.9" in file "tests/asciidoctor.bats"

2.3.9

Release published on the 2023-06-28 22:00:21 +0000 UTC at the url https://github.com/asciidoctor/asciidoctor-pdf/releases/tag/v2.3.9

This is a patch release in the 2.3.x release line that fixes alignment of image blocks in the multi-column layout and preserves the bottom end placement of the caption on a table when the unbreakable or breakable option is set.

## Distribution

- [RubyGem (asciidoctor-pdf)](https://rubygems.org/gems/asciidoctor-pdf)

## Changelog

### Bug Fixes

* correctly align block image in raster format in column when align is right or center and page columns are enabled (#2433)
* honor table caption end placement (`table-caption-end` theme key) when `unbreakable` (or `breakable`) option is set on table (#2434)

## Release meta

Released on: 2023-06-28
Released by: @mojavelinux
Release beer: Pappy Legma by Goat Patch Brewing Company

Logs: [resolved issues](https://github.com/asciidoctor/asciidoctor-pdf/issues?q=is%3Aissue+label%3Av2.3.9+is%3Aclosed) | [source diff](https://github.com/asciidoctor/asciidoctor-pdf/compare/v2.3.8...v2.3.9) | [gem diff](https://my.diffend.io/gems/asciidoctor/v2.3.8/v2.3.9)

## Credits

A very special thanks to all the **awesome** [supporters of the Asciidoctor OpenCollective campaign](https://opencollective.com/asciidoctor), who provide critical funding for the ongoing development of this project.

Update the key ASCIIDOCTOR_PDF_VERSION in the README.adoc file

Updated to content ":ASCIIDOCTOR_PDF_VERSION: 2.3.9" in file "README.adoc"

2.3.9

Release published on the 2023-06-28 22:00:21 +0000 UTC at the url https://github.com/asciidoctor/asciidoctor-pdf/releases/tag/v2.3.9

This is a patch release in the 2.3.x release line that fixes alignment of image blocks in the multi-column layout and preserves the bottom end placement of the caption on a table when the unbreakable or breakable option is set.

## Distribution

- [RubyGem (asciidoctor-pdf)](https://rubygems.org/gems/asciidoctor-pdf)

## Changelog

### Bug Fixes

* correctly align block image in raster format in column when align is right or center and page columns are enabled (#2433)
* honor table caption end placement (`table-caption-end` theme key) when `unbreakable` (or `breakable`) option is set on table (#2434)

## Release meta

Released on: 2023-06-28
Released by: @mojavelinux
Release beer: Pappy Legma by Goat Patch Brewing Company

Logs: [resolved issues](https://github.com/asciidoctor/asciidoctor-pdf/issues?q=is%3Aissue+label%3Av2.3.9+is%3Aclosed) | [source diff](https://github.com/asciidoctor/asciidoctor-pdf/compare/v2.3.8...v2.3.9) | [gem diff](https://my.diffend.io/gems/asciidoctor/v2.3.8/v2.3.9)

## Credits

A very special thanks to all the **awesome** [supporters of the Asciidoctor OpenCollective campaign](https://opencollective.com/asciidoctor), who provide critical funding for the ongoing development of this project.

Update the value of ARG asciidoctor_pdf_version in the Dockerfile

changed lines [16] of file "/tmp/updatecli/github/asciidoctor/docker-asciidoctor/Dockerfile"

2.3.9

Release published on the 2023-06-28 22:00:21 +0000 UTC at the url https://github.com/asciidoctor/asciidoctor-pdf/releases/tag/v2.3.9

This is a patch release in the 2.3.x release line that fixes alignment of image blocks in the multi-column layout and preserves the bottom end placement of the caption on a table when the unbreakable or breakable option is set.

## Distribution

- [RubyGem (asciidoctor-pdf)](https://rubygems.org/gems/asciidoctor-pdf)

## Changelog

### Bug Fixes

* correctly align block image in raster format in column when align is right or center and page columns are enabled (#2433)
* honor table caption end placement (`table-caption-end` theme key) when `unbreakable` (or `breakable`) option is set on table (#2434)

## Release meta

Released on: 2023-06-28
Released by: @mojavelinux
Release beer: Pappy Legma by Goat Patch Brewing Company

Logs: [resolved issues](https://github.com/asciidoctor/asciidoctor-pdf/issues?q=is%3Aissue+label%3Av2.3.9+is%3Aclosed) | [source diff](https://github.com/asciidoctor/asciidoctor-pdf/compare/v2.3.8...v2.3.9) | [gem diff](https://my.diffend.io/gems/asciidoctor/v2.3.8/v2.3.9)

## Credits

A very special thanks to all the **awesome** [supporters of the Asciidoctor OpenCollective campaign](https://opencollective.com/asciidoctor), who provide critical funding for the ongoing development of this project.

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