Return back to the original checkout SHA1

The upload-sarif action dislikes the change done by our rebase:

| No longer on merge commit, rewriting ref from refs/pull/3401/merge to refs/pull/3401/head.
| ...
| Uploading results
| Warning: commit not found
| Error: commit not found

container/cmd

@@ -96,6 +96,9 @@ if test "$GITHUB_EVENT_NAME" = 'pull_request'; then
     for subdir in $INPUT_SUBDIRECTORIES; do
         analyze_subdir "$subdir"
     done
+
+    # Return back to the previous git-sha1
+    git checkout "$GITHUB_SHA"
 else
     touch "$rootdir/output.sarif.err"
 fi