Update runtime container to Golang 1.21 (#188)

Author: mdehoog

Dockerfile

@@ -30,7 +30,7 @@ RUN git clone $REPO --branch $VERSION --single-branch . && \
 
 RUN go run build/ci.go install -static ./cmd/geth
 
-FROM golang:1.20
+FROM golang:1.21
 
 RUN apt-get update && \
     apt-get install -y jq curl supervisor && \