Use Node.js 16

Reasons to bump:

1. Both downstream repos use Node.js 16 now.
2. NPM 6 (bundled with Node.js 14) is slow to install Auspice from a
   GitHub commit reference. Later versions of NPM should fix this¹.

¹ npm/cli#4896

.github/workflows/make_pr_for_downstream_repo.yaml

@@ -47,7 +47,7 @@ jobs:
 
       - uses: actions/setup-node@v2
         with:
-          node-version: '14'
+          node-version: '16'
 
       - name: Checkout downstream repo
         uses: actions/checkout@v2