tests: Use a temporary file in the bookmarkfile tests

Rather than always writing to `out.xbel` in the build directory, which
could cause issues when running tests in parallel, or expecting the
tests to not touch the build directory.

Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
10 jobs for bookmarkfile-test-tmp in 28 minutes and 51 seconds (queued for 1 second)
Status Job ID Name Coverage
  Style Check
passed #1301498
check-todos

00:02:02

failed #1301497
allowed to fail
style-check-diff

00:01:57

 
  Build
passed #1301501
cross-android_api21_arm64

00:02:01

passed #1301502
cross-android_api28_arm64

00:01:18

passed #1301503
cross-mingw64

00:02:23

passed #1301500
debian-stable-x86_64

00:02:27

passed #1301499
fedora-x86_64

00:08:52

passed #1301504
win32-ps
msys2-mingw32

00:11:25

passed #1301505
win32-ps
vs2017-x64

00:08:32

 
  Coverage
passed #1301506
coverage

00:01:32

76.1%
 
Name Stage Failure
failed
style-check-diff Style Check
 #include <stdio.h>
#include <stdlib.h>
+#include <string.h>
+#include <time.h>

#define TEST_URI_0 "file:///abc/defgh/ijklmnopqrstuvwxyz"
#define TEST_URI_1 "file:///test/uri/1"
Cleaning up file based variables
ERROR: Job failed: exit code 1