Update Alpine to 3.20

Signed-off-by: Sanskar Jaiswal <jaiswalsanskar078@gmail.com>

Author: aryan9600

Dockerfile

@@ -21,7 +21,7 @@ RUN CGO_ENABLED=0 go build \
     -ldflags "-s -w -X github.com/fluxcd/flagger/pkg/version.REVISION=${REVISON}" \
     -a -o flagger ./cmd/flagger
 
-FROM alpine:3.19
+FROM alpine:3.20
 
 RUN apk --no-cache add ca-certificates