tests: Use a more interoperable path to bash

On systems that have undergone the /usr merge, /bin/bash and
/usr/bin/bash can be used interchangeably, but on systems where /bin and
/usr/bin are separate (such as Debian 11 or older), bash was traditionally
in /bin and there is no bash in /usr/bin.

Resolves: https://gitlab.gnome.org/GNOME/mutter/-/issues/2385
Signed-off-by: Simon McVittie <smcv@debian.org>
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2900>

.gitlab-ci/checkout-gnome-shell.sh

@@ -1,4 +1,4 @@
-#!/usr/bin/bash
+#!/bin/bash
 
 fetch() {
   local remote=$1

.gitlab-ci/download-coverity-tarball.sh

@@ -1,4 +1,4 @@
-#!/usr/bin/bash
+#!/bin/bash
 
 # We need a coverity token to fetch the tarball
 if [ -x $COVERITY_TOKEN ]

src/tests/kvm/run-kvm-test.sh

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

src/tests/kvm/virtme-run.sh

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

src/tests/x11-test.sh

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