meson: install test data

v2:
- do not install test-data if instal-tests=no
diff --git a/meson.build b/meson.build
index 60be100..ee886b8 100644
--- a/meson.build
+++ b/meson.build
@@ -1114,6 +1114,7 @@
 subdir('src/boot/efi')
 
 subdir('src/test')
+subdir('test')
 
 executable('systemd',
            systemd_sources,