Update version of checkout action from 2 to 3

This avoids a warning about a deprected node.js version (version 12).

Author: thomasspriggs

.github/workflows/models_library_pr.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
       - name: Setup Java environment
         uses: actions/setup-java@v2
         with: