tools: Ignore false-positive lintian error about po.html files not being source
tools: Ignore false-positive lintian error about po.html files not being source

These recently got > 250 lines for some languages. This is not source,
but built from po/*.po, and intended.

moraleslazaro/cockpit,mvollmer/cockpit,martinpitt/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,cockpituous/cockpit,cockpituous/cockpit,deryni/cockpit,moraleslazaro/cockpit,deryni/cockpit,garrett/cockpit,deryni/cockpit,cockpit-project/cockpit,mvollmer/cockpit,moraleslazaro/cockpit,garrett/cockpit,mvollmer/cockpit,garrett/cockpit,mvollmer/cockpit,mvollmer/cockpit,cockpituous/cockpit,deryni/cockpit,deryni/cockpit,cockpit-project/cockpit,moraleslazaro/cockpit,deryni/cockpit,moraleslazaro/cockpit,garrett/cockpit,moraleslazaro/cockpit,martinpitt/cockpit,garrett/cockpit,martinpitt/cockpit,moraleslazaro/cockpit,cockpituous/cockpit,cockpituous/cockpit,martinpitt/cockpit,martinpitt/cockpit,cockpituous/cockpit,deryni/cockpit