chore(deps): update alpine docker tag to v3.20.0

Dockerfile.armv6

@@ -8,6 +8,6 @@ RUN go mod download
 RUN CGO_ENABLED=0 go build -o /go/bin/splunk-mqtt
 
 # Now copy it into our base image.
-FROM alpine:3.17.2
+FROM alpine:3.20.0
 COPY --from=builder /go/bin/splunk-mqtt /splunk-mqtt
 CMD ["/splunk-mqtt"]