Make some scripts more portable

Change-Id: Ia89059eea51ca396a7c74143625ac9a6706de198
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/120773
Tested-by: Jenkins
Reviewed-by: Ilmari Lauhakangas <ilmari.lauhakangas@libreoffice.org>

setup_native/scripts/install_linux.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 #
 # This file is part of the LibreOffice project.
 #

setup_native/scripts/mac_install.script

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 #
 # This file is part of the LibreOffice project.
 #

setup_native/scripts/uninstall_linux.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 #
 # This file is part of the LibreOffice project.
 #