chore(deps): update dependency @antora/site-generator to v3.1.9

[renovate-bot]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
@antora/site-generator (source)	3.1.7 -> 3.1.9

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Release Notes

antora/antora (@​antora/site-generator)

### [`v3.1.9`](https://gitlab.com/antora/antora/compare/v3.1.8...v3.1.9) [Compare Source](https://gitlab.com/antora/antora/compare/v3.1.8...v3.1.9) ### [`v3.1.8`](https://gitlab.com/antora/antora/compare/v3.1.7...v3.1.8) [Compare Source](https://gitlab.com/antora/antora/compare/v3.1.7...v3.1.8)

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