Bump alpine from 3.20 to 3.21 (#278)

Dockerfile

@@ -22,7 +22,7 @@ ARG TARGETOS
 # Build
 RUN CGO_ENABLED=0 GOOS=$TARGETOS GOARCH=$TARGETARCH go build -a -o manager main.go
 
-FROM alpine:3.20
+FROM alpine:3.21
 
 # Install ipmitool required by the third party BMC lib.
 RUN apk add --upgrade ipmitool=1.8.19-r1