Adjust shell scripts to properly get bash from environment

ci.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 set -ex
 
 ./fmt.sh -- --check

renamesyms.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 set -e
 

tests/run_tests.sh

@@ -1,4 +1,4 @@
-#!/usr/bin/bash
+#!/usr/bin/env bash
 
 # Binaries that should generate the same output every time
 EXPECT_NAMES=(\