fix: Dockerfile to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-UPSTREAM-NODE-6564548

Dockerfile

@@ -1,4 +1,4 @@
-FROM node:20.11.1-alpine
+FROM node:20.12.1-alpine
 WORKDIR /usr/src/vault-cert-finder
 COPY . ./
 RUN yarn