chore(deps): pin dependencies (#20)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

Dockerfile

@@ -1,7 +1,7 @@
-FROM caddy:2.9.1-builder-alpine AS builder
+FROM caddy:2.9.1-builder-alpine@sha256:ca7cf1f32bfd454db7517326d4282b6aa9794843e492f5d29a051d8758874d0b AS builder
 
 RUN xcaddy build --with github.com/caddy-dns/cloudflare
 
-FROM caddy:2.9.1-alpine
+FROM caddy:2.9.1-alpine@sha256:1131a7f215fdcbf0543a7096fceddd2304f14608b3c2c852224f3ee6b3dd6a80
 
 COPY --from=builder /usr/bin/caddy /usr/bin/caddy