DEB_BUILD_OPTIONS should be a space-separated list in build-script

In this file,

https://salsa.debian.org/salsa-ci-team/pipeline/-/blob/master/salsa-ci.yml#L178

   test -z "${HOST_ARCH}" || export DEB_BUILD_OPTIONS=nocheck${DEB_BUILD_OPTIONS:+,}${DEB_BUILD_OPTIONS}

in the case of crossbuilding, the DEB_BUILD_OPTIONS env. var uses the "," separator.

This can result in such an error

dpkg-buildpackage: warning: invalid flag in DEB_BUILD_OPTIONS: nocheck,noautodbgsym

The values should be space separated

From dpkg-buildpackage manpage:

       DEB_BUILD_OPTIONS
              If set, it will contain a space-separated list of options
              that might affect the build process in debian/rules, and
              the behavior of some dpkg commands.