Update traefik Docker tag to v1.7.31

[renovate[bot]]

This PR contains the following updates:

Package	Update	Change
traefik	patch	v1.7.30-alpine -> v1.7.31-alpine

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Release Notes

containous/traefik

### [`v1.7.31`](https://togithub.com/containous/traefik/releases/v1.7.31) [Compare Source](https://togithub.com/containous/traefik/compare/v1.7.31...v1.7.31) **Bug fixes:** - **\[acme,k8s]** acme: add support of preferredchain in Traefik v1 ([#​8482](https://togithub.com/traefik/traefik/pull/8482) by [ldez](https://togithub.com/ldez)) ### [`v1.7.31`](https://togithub.com/containous/traefik/releases/v1.7.31) [Compare Source](https://togithub.com/containous/traefik/compare/v1.7.30...v1.7.31) **Bug fixes:** - **\[acme,k8s]** acme: add support of preferredchain in Traefik v1 ([#​8482](https://togithub.com/traefik/traefik/pull/8482) by [ldez](https://togithub.com/ldez))

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