chore(deps): update nginx docker tag to v1.31

[chrisns]

This PR contains the following updates:

Package	Type	Update	Change
nginx	final	minor	1.27-alpine → 1.31-alpine

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[chrisns]

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[chrisns]

Superseded by new renovate grouping (per-scenario + npm-web + github-actions). See #357 for the config change. This PR's dep, if still pending, will be re-opened inside the appropriate grouped PR on the next renovate cycle.