data: Fix tests for desktop and appstream files

data/meson.build

@@ -7,8 +7,9 @@ install_data('sm.puri.Calls.desktop',
 desktop_utils = find_program('desktop-file-validate', required: false)
 if desktop_utils.found()
   test('Validate desktop file', desktop_utils,
-        args: ['sm.puri.Calls.desktop']
-    )
+       args: [join_paths(meson.current_source_dir(),
+                         'sm.puri.Calls.desktop')
+             ])
 endif
 
 # Appdata file
@@ -19,8 +20,10 @@ install_data('sm.puri.Calls.appdata.xml',
 appstream_util = find_program('appstream-util', required: false)
 if appstream_util.found()
   test('Validate appstream file', appstream_util,
-        args: ['validate-relax', 'sm.puri.Calls.appdata.xml']
-    )
+       args: ['validate-relax',
+              join_paths(meson.current_source_dir(),
+                         'sm.puri.Calls.appdata.xml')
+             ])
 endif
 
 # Icons