build(deps): update caddy docker tag to v2.7.3

Author: renovate[bot]

caddy/Dockerfile

@@ -1,9 +1,9 @@
-FROM caddy:2.6.4-builder-alpine AS builder
+FROM caddy:2.7.3-builder-alpine AS builder
 
 RUN xcaddy build \
     --with github.com/caddy-dns/cloudflare
 
-FROM caddy:2.6.4-alpine
+FROM caddy:2.7.3-alpine
 
 COPY Caddyfile cloudflare-origin-pull-ca.pem /etc/caddy/
 COPY --from=builder /usr/bin/caddy /usr/bin/caddy