Fix shellcheck lint in tools/gpuci_retry (#38)

* Empty commit to test CI

* Add blank lines to tools scripts to run CI

* Revert "Add blank lines to tools scripts to run CI"

This reverts commit a83b035.

* Apply `shellcheck` fixes to `tools` scripts

CI started failing on `main`. Looks like this was due to a `shellcheck`
failure. This applies the fix proposed by `shellcheck` to clear CI
issues.

tools/gpuci_retry

@@ -39,7 +39,7 @@ function gpuci_retry {
           (( retries < max_retries )); do
       ((retries++))
       gpuci_logger "gpuci_retry: retry ${retries} of ${max_retries} | exit code: (${retcode}) -> sleeping for ${sleep_interval} seconds..."
-      sleep ${sleep_interval}
+      sleep "${sleep_interval}"
       gpuci_logger "gpuci_retry: sleep done -> retrying..."
 
       ${command} "$@"