test: move wireplumber tests into a 'wp' subfolder

tests/meson.build

-common_deps = [gobject_dep, gio_dep, wp_dep, pipewire_dep]
-common_env = [
-  'G_TEST_SRCDIR=@0@'.format(meson.current_source_dir()),
-  'G_TEST_BUILDDIR=@0@'.format(meson.current_build_dir()),
-]
-
-test(
-  'test-properties',
-  executable('test-properties', 'properties.c', dependencies: common_deps),
-  env: common_env,
-)
-
-test(
-  'test-proxy',
-  executable('test-proxy', 'proxy.c', dependencies: common_deps),
-  env: common_env,
-)
+subdir('wp')

tests/wp/meson.build

+common_deps = [gobject_dep, gio_dep, wp_dep, pipewire_dep]
+common_env = [
+  'G_TEST_SRCDIR=@0@'.format(meson.current_source_dir()),
+  'G_TEST_BUILDDIR=@0@'.format(meson.current_build_dir()),
+]
+
+test(
+  'test-properties',
+  executable('test-properties', 'properties.c', dependencies: common_deps),
+  env: common_env,
+)
+
+test(
+  'test-proxy',
+  executable('test-proxy', 'proxy.c', dependencies: common_deps),
+  env: common_env,
+)