CI: Consistently use actions/checkout@v2

v2 is the current version of the checkout action and faster than v1.
diff --git a/.github/workflows/openssl-nodeprecated.yml b/.github/workflows/openssl-nodeprecated.yml
index e62dbf0..e423f58 100644
--- a/.github/workflows/openssl-nodeprecated.yml
+++ b/.github/workflows/openssl-nodeprecated.yml
@@ -21,7 +21,7 @@
   test:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: Install VTest
       run: |
         scripts/build-vtest.sh