ci: use node 18 instead of 12

Author: Kai Volland

.github/workflows/on-pull-request.yml

@@ -8,7 +8,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [12.x, 14.x, 16.x]
+        node-version: [14.x, 16.x, 18.x]
 
     steps:
     - name: Checkout sources

.github/workflows/on-push-master.yml

@@ -11,7 +11,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [12.x, 14.x, 16.x]
+        node-version: [14.x, 16.x, 18.x]
 
     steps:
     - name: Checkout sources