Satisfy Linux multiarch Python tooling.

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

@@ -46,6 +46,7 @@ case "$target" in
         # They are unrelated to the build, but make apt replace native Python
         # while resolving foreign-architecture development packages.
         sudo env DEBIAN_FRONTEND=noninteractive apt-get remove -y mercurial python3-importlib-metadata python3-jwt
+        install_packages python3 python3-typing-extensions
 
         sudo dpkg --add-architecture amd64
         {