CI: Test Node 14 with windows-2019 image

Node 14 is pretty old by now.

Node 14 latest was Node v14.21.3, which came with npm 6.14.8,
which came with node-gyp v5.1.1.

node-gyp v5.1.1 doesn't support Cisual Studio 2022, which is the most
recent version and is included in the windows-latest GitHub-hosted
runner for GitHub Actions.

Using the windows-2019 GitHub-hosted runner for Node 14 on Windows
should work, since old node-gyp v5.1.1 should work with Visual Studio
2019... Hopefully.

.github/workflows/ci.yml

@@ -18,6 +18,12 @@ jobs:
           - 14
           - 16
           - 18
+        exclude:
+          - os: windows-latest
+            node_version: 14
+        include:
+          - os: windows-2019
+            node_version: 14
     name: Node ${{ matrix.node_version }} on ${{ matrix.os }}
 
     steps: