Update the dependency on actions/checkout.

The new version uses Node.js 16 (eliminating warnings about Node.js 12
deprecation).

Author: philr

.github/workflows/tests.yml

@@ -47,7 +47,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     continue-on-error: ${{ matrix.experimental }}
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - if: startsWith(matrix.ruby, '1.8') || (startsWith(matrix.ruby, '1.9') && startsWith(matrix.os, 'windows')) || (startsWith(matrix.ruby, '2.0') && startsWith(matrix.os, 'windows') && matrix.architecture == 'x86') || startsWith(matrix.ruby, 'jruby-1.7') || startsWith(matrix.ruby, 'jruby-9.0')
         uses: philr/setup-ruby@legacy-v1
         with: