Fix Ubuntu x64 package sources.

.gitea/scripts/install-linux-build-dependencies.sh

@@ -33,6 +33,15 @@ case "$target" in
             exit 1
         fi
 
+        native_sources=/etc/apt/sources.list.d/ubuntu.sources
+        if [ ! -f "$native_sources" ]; then
+            echo "the x64 release build requires Ubuntu's deb822 package sources" >&2
+            exit 1
+        fi
+        sudo sed -i \
+            '/^Architectures:/d; /^Types: deb$/a Architectures: arm64' \
+            "$native_sources"
+
         sudo dpkg --add-architecture amd64
         {
             printf '%s\n' \