[CI/Build] Add shell script linting using shellcheck (#7925)

Signed-off-by: Russell Bryant <rbryant@redhat.com>

.buildkite/run-xpu-test.sh

@@ -1,3 +1,5 @@
+#!/bin/bash
+
 # This script build the CPU docker image and run the offline inference inside the container.
 # It serves a sanity check for compilation and basic model usage.
 set -ex