Fix docs install

While the generated package worked, the workaround modified the source
which apparently shouldn't be done.

This patch fixes the workaround by using a temporary directory to create
the documentation before using dh_installdocs to install it.
3 jobs for debian/1.1-1 in 6 minutes and 49 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Test
passed #387835
integration_test

00:04:59

passed #387836
integration_test_latest

00:05:20

 
  Docker Image
failed #387837
image_build

00:01:27

 
Name Stage Failure
failed
image_build Docker Image
WARNING! Your password will be stored unencrypted in /root/.docker/config.json.
Configure a credential helper to remove this warning. See
https://docs.docker.com/engine/reference/commandline/login/#credentials-store

Login Succeeded
$ docker build -t $CI_REGISTRY_IMAGE:$CI_BUILD_REF_NAME -f docker/Dockerfile .
invalid argument "registry.salsa.debian.org/go-team/packages/chasquid:debian/1.1-1" for "-t, --tag" flag: invalid reference format
See 'docker build --help'.
ERROR: Job failed: exit code 125