Bump plantuml-markdown from 3.7.2 to 3.7.3 in /CI (#1193)

Bumps [plantuml-markdown](https://github.com/mikitex70/plantuml-markdown) from 3.7.2 to 3.7.3.
- [Release notes](https://github.com/mikitex70/plantuml-markdown/releases)
- [Changelog](https://github.com/mikitex70/plantuml-markdown/blob/master/CHANGELOG.md)
- [Commits](https://github.com/mikitex70/plantuml-markdown/compare/3.7.2...3.7.3)

---
updated-dependencies:
- dependency-name: plantuml-markdown
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

CI/requirements.txt

@@ -5,4 +5,4 @@ mkdocs-exclude==1.0.2
 mkdocs-redirects==1.2.0
 mkdocs-git-revision-date-localized-plugin==1.1.0
 mkdocs-minify-plugin==0.5.0
-plantuml-markdown==3.7.2
+plantuml-markdown==3.7.3