Fix CI failure on Windows (#142)

At some point in last year, label `windows-latest` runs windows-2022
runner. However node-gyp does not seem to support the latest Visual
Studio. It is causing a current CI failure on Windows node.
Using `windows-2019` label fixes the issue.

Author: rhysd

.github/workflows/ci.yml

@@ -18,7 +18,7 @@ jobs:
       - run: npm install
       - run: npm test
   test_windows:
-    runs-on: windows-latest
+    runs-on: windows-2019
     steps:
       - uses: actions/checkout@v2
       - uses: actions/setup-node@v2