chore(deps): update docker.io/library/golang docker tag to v1.20

Dockerfile

@@ -5,7 +5,7 @@ RUN npm install && env NODE_OPTIONS=--openssl-legacy-provider ./node_modules/.bi
 
 # Debian bullseye can't build gostatic due to its strict dependency
 # on Go >1.17, so we build it separately.
-FROM docker.io/library/golang:1.19 AS gobuild
+FROM docker.io/library/golang:1.20 AS gobuild
 RUN go install github.com/piranha/gostatic@latest
 RUN go install git.autistici.org/ai/webtools/cmd/jsonsubst@latest
 RUN go install git.autistici.org/ai/webtools/cmd/sitesearch@latest