treewide: more portable bash shebangs

As in 2a5fcfae02
and in 3e67e5c992
using /usr/bin/env allows bash to be looked up in PATH
rather than being hard-coded.

As with the previous changes the same arguments apply
- distributions have scripts to rewrite shebangs on installation and
  they know what locations to rely on.
- For tests/compilation we should rather rely on the user to have setup
  there PATH correctly.

In particular this makes testing from git easier on NixOS where do not provide
/bin/bash to improve compose-ability.

src/kernel-install/00-entry-directory.install

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 # -*- mode: shell-script; indent-tabs-mode: nil; sh-basic-offset: 4; -*-
 # ex: ts=8 sw=4 sts=4 et filetype=sh
 

src/kernel-install/50-depmod.install

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 # -*- mode: shell-script; indent-tabs-mode: nil; sh-basic-offset: 4; -*-
 # ex: ts=8 sw=4 sts=4 et filetype=sh
 

src/kernel-install/90-loaderentry.install

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 # -*- mode: shell-script; indent-tabs-mode: nil; sh-basic-offset: 4; -*-
 # ex: ts=8 sw=4 sts=4 et filetype=sh
 

src/kernel-install/kernel-install

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 # -*- mode: shell-script; indent-tabs-mode: nil; sh-basic-offset: 4; -*-
 # ex: ts=8 sw=4 sts=4 et filetype=sh
 # SPDX-License-Identifier: LGPL-2.1+