Remove unsupported Node.js versions

Author: piecioshka

.github/workflows/testing.yml

@@ -16,7 +16,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [13.x, 14.x, 16.x, 18.x]
+        node-version: [13.x, 14.x, 16.x]
 
     steps:
     - uses: actions/checkout@v3