fix(CI): on Windows call rustup target add x86_64-pc-windows-gnu

Author: nickysn

.github/workflows/ci.yml

@@ -47,6 +47,7 @@ jobs:
         run: |
           if [[ "$RUNNER_OS" == "Windows" ]]; then
             pacman -S --noconfirm mingw-w64-ucrt-x86_64-capnproto
+            rustup target add x86_64-pc-windows-gnu
           #  ridk enable
           fi
           just build-extension