ci: Switch to actions/checkout@v4 (#31379)

This change also removes the use of `fetch-depth: 2` where it isn't
necessary. These were likely copy-and-pasted from other workflows.

.github/workflows/mac-wpt.yml

@@ -30,17 +30,14 @@ jobs:
       matrix:
         chunk_id: [1, 2, 3, 4, 5]
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         if: github.event_name != 'pull_request_target'
-        with:
-          fetch-depth: 2
       # This is necessary to checkout the pull request if this run was triggered via a
       # `pull_request_target` event.
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         if: github.event_name == 'pull_request_target'
         with:
           ref: refs/pull/${{ github.event.number }}/head
-          fetch-depth: 2
       - uses: actions/download-artifact@v4
         with:
           name: ${{ inputs.profile }}-binary-macos