[gnome-builder/wip/gtk4-port] plugins/meson: use new variable name for test sources

[Christian Hergert <chergert src gnome org>]

commit d7d45194b51782cb5bc8b90528acc88836bfcc62
Author: Christian Hergert <christian hergert me>
Date:   Wed Jun 15 15:06:47 2022 -0700

    plugins/meson: use new variable name for test sources

 src/plugins/meson/meson.build | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/src/plugins/meson/meson.build b/src/plugins/meson/meson.build
index 58b14ee10..92ef1b935 100644
--- a/src/plugins/meson/meson.build
+++ b/src/plugins/meson/meson.build
@@ -31,14 +31,14 @@ plugin_meson_resources = gnome.compile_resources(
 
 plugins_sources += plugin_meson_resources
 
-test_sources += files([
+test_meson_sources = files([
   'test-meson-build-system.c',
   'gbp-meson-build-system.c',
   'gbp-meson-toolchain.c',
   'gbp-meson-utils.c',
 ])
 
-test_meson = executable('test-meson', test_sources,
+test_meson = executable('test-meson', test_meson_sources,
         c_args: test_cflags,
   dependencies: [ libide_foundry_dep, libide_terminal_dep ],
 )