ci: pin node 16 version

Author: castarco

.github/workflows/tests.yml

@@ -18,7 +18,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [14.x, 16.x, 17.x]
+        node-version: [14.x, '16.4.0', 17.x]
 
     steps:
     - uses: actions/checkout@v2