package/ci: MSYS, the ancient curses seem to have returned.

package/ci/appveyor-lcov.sh

@@ -9,7 +9,10 @@ curl -O http://repo.msys2.org/msys/x86_64/msys2-keyring-r21.b39fb11-1-any.pkg.ta
 pacman-key --verify msys2-keyring-r21.b39fb11-1-any.pkg.tar.xz.sig
 pacman -U --noconfirm msys2-keyring-r21.b39fb11-1-any.pkg.tar.xz
 
-pacman -Sy --noconfirm mingw-w64-x86_64-perl
+# Newer packages use zstd, but this old pacman has no idea what that is.
+# Download the last perl that's still compressed with xz.
+curl -O http://repo.msys2.org/msys/x86_64/perl-5.30.2-1-x86_64.pkg.tar.xz
+pacman -U --noconfirm perl-5.30.2-1-x86_64.pkg.tar.xz
 
 # mingw lcov package is empty, so download and use it manually
 # https://github.com/appveyor/ci/issues/1628