CI: Pre-warm node headers cache for node-gyp on Windows

Older node-gyp was buggier/had a race condition
when trying to grab and cache the node headers
multiple times in parallel. Workaround is to install once
ahead of time, or upgrade to newer node-gyp.

Author: DeeDeeG

.github/workflows/ci.yml

@@ -24,6 +24,9 @@ jobs:
       - name: Install windows-build-tools
         if: ${{ matrix.os == 'windows-latest' }}
         run: npm config set msvs_version 2019
+      - name: Pre-warm the node headers cache for node-gyp
+        if: ${{ runner.os == 'Windows' }}
+        run: npx node-gyp install
       - name: Install dependencies
         run: npm i
       - name: Run tests