Checkout PR changes for testing instead of main

This solves the issue where the github workflow was using the latest
commit from main instead of the new commit from the PR.

Issue came about because we need to use pull_request_target to use a
secret in the workflow.

This change uses github.event.pull_request.head.sha to get the PR
changes to test now

Assisted-by: Gemini
Signed-off-by: Adam Scerra <ascerra@redhat.com>

Author: ascerra

.github/workflows/checks-sealights.yaml

@@ -51,11 +51,15 @@ jobs:
           echo "Invalid context for this workflow run. Exiting."
           exit 1
 
-      - name: Checkout repository
+      - name: Checkout PR Head
         uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
-          # Needed in hack/derive-version.sh
-          fetch-depth: 0
+          ref: ${{ github.event.pull_request.head.sha }}
+          token: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Show git sha and commit subject
+        run: git log --oneline -n1
+
 
       - name: Restore Cache
         uses: actions/cache/restore@d4323d4df104b026a6aa633fdb11d772146be0bf # v4.2.2