Merge branch 'renovate/golang-1.x' into 'master'

Update golang Docker tag to v1.21.1

See merge request !41

Dockerfile

@@ -12,7 +12,7 @@ RUN find /src/assets -type f -regextype egrep -regex '.*\.(css|js|svg|html)' -pr
 RUN find /src/assets -type f -regextype egrep -regex '.*\.(css|js|svg|html)' -print \
     | xargs gzip -9k
 
-FROM golang:1.18.0 AS build
+FROM golang:1.21.1 AS build
 ADD . /src
 WORKDIR /src
 COPY --from=precompress /src/assets /src/assets