fix: use bash, not sh, for code_style.sh script (#1022)

The script uses "set -o", which doesn't exist in vanilla sh, causing
failure on systems that bind sh to dash rather than bash. This PR makes
the bash requirement explicit.

code_style.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/usr/bin/env bash
 
 set -euo pipefail