build: Switch to the portable shebang in scripts

Signed-off-by: Fabian Bornschein <fabiscafe@mailbox.org>

package-release.sh

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

setup_vkd3d_proton.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 # default directories
 vkd3d_lib32=${vkd3d_lib32:-"x86"}