build: Avoid a Meson deprecation warning

Using an empty `configuration_data` object to copy a configuration file
is deprecated since Meson 0.47 (released July 2018); the equivalent
behaviour is available by using `copy: true`.

meson.build

@@ -7,7 +7,7 @@ project('gtk+', 'c',
           # https://github.com/mesonbuild/meson/issues/2289
           'c_std=gnu99',
         ],
-        meson_version : '>= 0.43.0',
+        meson_version : '>= 0.48.0',
         license: 'LGPLv2.1+')
 
 glib_major_req = 2

testsuite/tools/meson.build

@@ -8,7 +8,7 @@ if bash.found()
   foreach t : ['simplify', 'settings']
     configure_file(output: t,
                    input: '@0@.in'.format(t),
-                   configuration: configuration_data(),
+                   copy: true,
                    install: get_option('install-tests'),
                    install_dir: testexecdir)
     test(t, bash,