ci(debian): add gierens as .deb codeowner

Signed-off-by: Christina Sørensen <christina@cafkafk.com>

.github/CODEOWNERS

@@ -38,3 +38,7 @@ Cargo.lock @cafkafk
 devtools/* @cafkafk
 tests/* @cafkafk
 xtests/* @cafkafk
+
+# Debian files
+devtools/deb-package.sh @gierens
+deb.asc @gierens