Fix Windows CI on Node 20 and 22 by using a current node-gyp

The windows-latest image ships Visual Studio 18. The node-gyp bundled with
npm on Node 20 and 22 does not recognise it and fails configure with
'find VS unknown version "undefined"'; Node 24 already carries a new enough
node-gyp, which is why only those two cells failed.

Install node-gyp@latest on Windows runners and point npm at it. Also document
the same workaround for users, who hit this whenever they pair Node 20 or 22
with Visual Studio 2026.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: mschmicking

.github/workflows/ci.yml

@@ -25,6 +25,16 @@ jobs:
         with:
           node-version: ${{ matrix.node }}
 
+      # The node-gyp bundled with npm on Node 20 and 22 cannot detect Visual
+      # Studio 18, which is what the windows-latest image now ships, and bails
+      # with 'unknown version "undefined"'. Node 24 already carries a new enough
+      # node-gyp. Point npm at a current one so every Node version can build.
+      - name: Use a current node-gyp on Windows
+        if: runner.os == 'Windows'
+        run: |
+          npm install -g node-gyp@latest
+          npm config set node_gyp "$(npm prefix -g)/node_modules/node-gyp/bin/node-gyp.js"
+
       # Compiles the addon along with the vendored Lua and LuaFileSystem sources.
       - name: Install and build
         run: npm install

README.md

@@ -21,6 +21,15 @@ The addon is compiled at install time, so you need a working C/C++ toolchain:
 Nothing else. Earlier versions needed you to build and install LuaJIT yourself on Linux; that is
 no longer the case.
 
+> **Windows with Visual Studio 2026:** the `node-gyp` bundled with Node.js 20 and 22 cannot detect
+> that version and fails with `find VS unknown version "undefined"`. Node.js 24 is unaffected. On
+> Node 20 or 22, point npm at a current node-gyp:
+>
+> ```
+> npm install -g node-gyp@latest
+> npm config set node_gyp "%APPDATA%\npm\node_modules\node-gyp\bin\node-gyp.js"
+> ```
+
 ## Quick start
 
 ```javascript