ci-license-scan: Remove non ascii chars from debian override

The version of scan-copyrights from Trixie tries to parse the copyright
data to provide cleaner information. At the same time, this version
is more strict on the data use to fill debian/fill.copyright.blanks.yml,
and in case of non ascii characters the tool exits with error.

Since ci-license-scan fill the file with data, make sure that it only
adds ascii characters to the copyright.

Signed-off-by: Walter Lozano <walter.lozano@collabora.com>