Update to actions/checkout@v3 (PHP-8.1)

see 629fcb6

Author: TimWolla

.github/workflows/nightly.yml

@@ -469,7 +469,7 @@ jobs:
     runs-on: ubuntu-20.04
     steps:
       - name: git checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
         with:
           ref: ${{ matrix.branch.ref }}
       - name: apt