Use Node.js 16.x for webpack related actions.

- Node.js 18.x needs a newer webpack and related tools. Will return to
  18.x when the tooling is updated.

Author: davidlehn

.github/workflows/main.yml

@@ -41,7 +41,7 @@ jobs:
     timeout-minutes: 10
     strategy:
       matrix:
-        node-version: [18.x]
+        node-version: [16.x]
         bundler: [webpack, browserify]
     steps:
     - uses: actions/checkout@v3
@@ -62,7 +62,7 @@ jobs:
     timeout-minutes: 10
     strategy:
       matrix:
-        node-version: [18.x]
+        node-version: [16.x]
     steps:
     - uses: actions/checkout@v3
     - name: Use Node.js ${{ matrix.node-version }}