Update docker.io/library/caddy Docker tag to v2.7.3

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
docker.io/library/caddy	final	patch	2.7.2-alpine -> 2.7.3-alpine
docker.io/library/caddy	stage	patch	2.7.2-builder-alpine -> 2.7.3-builder-alpine

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