Use Bash for release scripts using non-POSIX features

A script using "declare -a" can't use /bin/sh as it's non-POSIX and not
supported by e.g. Dash which is /bin/sh on Debian systems.

build/tools/post-release.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/bin/bash
 
 # Exit immediately if a command exits with a non-zero status.
 set -e

build/tools/pre-release.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/bin/bash
 
 # build a list of English locales
 declare -a locale_list=("en_GB" "en_US")