fix: cmd/pipecd/Dockerfile to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-ALPINE321-MUSL-8720634
- https://snyk.io/vuln/SNYK-ALPINE321-MUSL-8720634
- https://snyk.io/vuln/SNYK-ALPINE321-OPENSSL-8690014
- https://snyk.io/vuln/SNYK-ALPINE321-OPENSSL-8690014
- https://snyk.io/vuln/SNYK-ALPINE321-OPENSSL-8710358

Author: snyk-bot

cmd/pipecd/Dockerfile

@@ -29,7 +29,7 @@ COPY . ./
 
 RUN make build/go MOD=pipecd
 
-FROM alpine:3.21.0
+FROM alpine:3.21.3
 
 ARG GOOGLE_CLOUD_SDK_VERSION=477.0.0