chore(deps): update solidnerd/bookstack docker tag to v0.31.6

This MR contains the following updates:

Package	Update	Change
solidnerd/bookstack	minor	0.29.2 -> 0.31.6

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Release Notes

solidnerd/docker-bookstack

v0.31.6

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• 1b3eef9 - upgrade to 0.31.6 (#​227)

v0.31.4

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• 0f2c074 - upgrade to 0.31.4 (#​224)
• b6ac6e2 - chore(deps): update mysql docker tag to v5.7.33 (#​225)

v0.31.3

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• f5f3508 - upgrade to 0.31.3 (#​223)

v0.30.7

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• 311e798 - chore(ci): update github actions
• 164730c - upgrade to 0.30.7 (#​222)

v0.30.4

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Features 🌈

• upgrade bookstack to 0.30.4 by #​217

v0.30.2

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Features 🌈

• upgrade bookstack to 0.30.2 by #​209

Fixes 🐞

• Set composer version to 1.10.16 #​215

v0.29.3

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Features 🌈 upgrade bookstack to 0.29.3

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