Bump alpine from 3.15.4 to 3.18.5 in /build

Bumps alpine from 3.15.4 to 3.18.5.

---
updated-dependencies:
- dependency-name: alpine
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

build/Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:3.18.2
+FROM alpine:3.18.5
 
 RUN apk --no-cache add \
     ca-certificates

build/Dockerfile-multiarch

@@ -17,7 +17,7 @@ ADD . /build
 RUN ldFlags="-s -X main.Version=$(git describe --abbrev=0 --tags) -X main.GitCommit=$(git rev-parse --short HEAD) -X main.BuildDate=$(date +%Y-%m-%d-%H:%M)"; \
     CGO_ENABLED=0 GOOS=linux GOARCH=${TARGETARCH} go build -o bin/linux/${TARGETARCH}/${BINARY_NAME} -ldflags "${ldFlags}" ${MAIN_PKG}
 
-FROM alpine:3.15.4
+FROM alpine:3.18.5
 
 RUN apk --no-cache add \
     ca-certificates