[repository sources] copy source configuration: source's __init__ modify it while config.sources() return a cached dictionary which shouldn't be modified
This causes pb since f8aa87a773b2 (though it's unclear why it hasn't been a problem before).
Closes #2521848
debian/tmp/usr/lib/PY_VERSION/site-packages/cubicweb/server/ usr/lib/PY_VERSION/site-packages/cubicweb
debian/tmp/usr/lib/PY_VERSION/site-packages/cubicweb/hooks/ usr/lib/PY_VERSION/site-packages/cubicweb
debian/tmp/usr/lib/PY_VERSION/site-packages/cubicweb/sobjects/ usr/lib/PY_VERSION/site-packages/cubicweb
debian/tmp/usr/lib/PY_VERSION/site-packages/cubicweb/schemas/ usr/lib/PY_VERSION/site-packages/cubicweb
debian/tmp/usr/share/cubicweb/migration/ usr/share/cubicweb/