ci: Fix try-label failure of media-examples (#43347)

Testing: Not tested, it's difficult to test try-label related changes.
The fix is trivial though.
Fixes: #43345

Signed-off-by: Jonathan Schwender <schwenderjonathan@gmail.com>

.github/workflows/linux.yml

@@ -390,6 +390,13 @@ jobs:
         if: github.event_name != 'pull_request_target'
         with:
           fetch-depth: 1
+      # This is necessary to checkout the pull request if this run was triggered via a
+      # `pull_request_target` event.
+      - uses: actions/checkout@v5
+        if: github.event_name == 'pull_request_target'
+        with:
+          ref: ${{ github.event.pull_request.head.sha }}
+          fetch-depth: 1
       - name: Change Mirror Priorities
         uses: ./.github/actions/apt-mirrors
       - name: Install Dependencies