Bump crystallang/crystal from 1.12.2-alpine to 1.16.2-alpine in /docker (#5290)

Bumps crystallang/crystal from 1.12.2-alpine to 1.16.2-alpine.

---
updated-dependencies:
- dependency-name: crystallang/crystal
  dependency-version: 1.16.2-alpine
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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docker/Dockerfile

@@ -1,4 +1,4 @@
-FROM crystallang/crystal:1.12.2-alpine AS builder
+FROM crystallang/crystal:1.16.2-alpine AS builder
 
 RUN apk add --no-cache sqlite-static yaml-static