Update pull.yml to use actions/checkout@v4

this is required, since v1 and v2 are deprecated
see https://github.blog/changelog/2024-02-13-deprecation-notice-v1-and-v2-of-the-artifact-actions/

Author: csiblock

.github/workflows/pull.yml

@@ -18,7 +18,7 @@ jobs:
     # Steps represent a sequence of tasks that will be executed as part of the job
     steps:
       # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
 
       # The same command that users can use locally is used to build documentation.
       - name: Build documentation