tests: add missing proxy-test

This was probably lost during a rebase.

Signed-off-by: Simon Ser <contact@emersion.fr>

tests/meson.build

@@ -146,6 +146,10 @@ tests = {
 		'headers-protocol-core-test.c',
 	],
 	'os-wrappers-test': [],
+	'proxy-test': [
+		wayland_client_protocol_h,
+		wayland_server_protocol_h,
+	],
 }
 
 foreach test_name, test_extra_sources: tests