ci: include node version 21 in matrix

Author: luisaveiro

.github/workflows/pull-request.yml

@@ -61,7 +61,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [18.x, 20.x]
+        node-version: [18.x, 20.x, 21.x]
 
     steps:
       - name: Checkout the Git repository