misc: use /usr/bin/env in scripts

This patch continues the work to support NixOS and others non-FHS
distributions by replacing instances of `/bin/bash` with
`/usr/bin/env bash`, which works correctly in more systems than the
former.

Signed-off-by: Luis Holanda <luiscmholanda@gmail.com>

release

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 set -xeuo pipefail
 
 sign=(-u motiejus@jakstys.lt)