Update node version in actions

Author: martenrichter

.github/workflows/libtest-linux.yml

@@ -30,7 +30,7 @@ jobs:
       - name: Set up NodeJS
         uses: actions/setup-node@v4
         with:
-          node-version: 18
+          node-version: 20
 
       - name: Install dependencies
         run:  npm install --ignore-scripts

.github/workflows/libtest-macos.yml

@@ -30,7 +30,7 @@ jobs:
       - name: Set up NodeJS
         uses: actions/setup-node@v4
         with:
-          node-version: 18
+          node-version: 20
 
       - name: Install dependencies
         run: npm install --ignore-scripts

.github/workflows/libtest-windows.yml

@@ -33,7 +33,7 @@ jobs:
       - name: Set up NodeJS
         uses: actions/setup-node@v4
         with:
-          node-version: 18
+          node-version: 20
 
       - name: Install dependencies
         run: npm install --ignore-scripts