tools: Fix Copyright: continuation lines in debian/copyright
tools: Fix Copyright: continuation lines in debian/copyright

Fix the join pattern to get proper indentation of continuation lines
instead of trailing spaces.

mvollmer/cockpit,cockpit-project/cockpit,mvollmer/cockpit,martinpitt/cockpit,mvollmer/cockpit,cockpit-project/cockpit,martinpitt/cockpit,martinpitt/cockpit,mvollmer/cockpit,mvollmer/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,martinpitt/cockpit,martinpitt/cockpit