.github: install nsis for Windows CI runners

Seems it's not preinstalled anymore.

Author: bk138

.github/workflows/ci.yml

@@ -30,6 +30,10 @@ jobs:
           brew uninstall --ignore-dependencies gnutls libgcrypt
           brew install wxwidgets@3.2
       - name: Install Windows Build Dependencies
+        if: ${{ matrix.os == 'windows-latest' }}
+        run: |
+          choco install nsis
+      - name: Install vcpkg Windows Build Dependencies
         if: ${{ matrix.os == 'windows-latest' }}
         uses: johnwason/vcpkg-action@v6
         id: vcpkg