debian: override the new lintian's public-upstream-key-in-native-package

Signed-off-by: Mattia Rizzolo <mattia@debian.org>

debian/source/lintian-overrides

 # This will mainly be used to double check that what we upload to Debian
 # is also in our "archive".
 debian-watch-file-in-native-package
+
+# We like to share our own keys for others to check the released signature.
+public-upstream-key-in-native-package