[test] allow only a single shared display to avoid egl errors

test/api/annotations.test.cpp

@@ -30,7 +30,7 @@ std::unique_ptr<style::Image> namedMarker(const std::string& name) {
 class AnnotationTest {
 public:
     util::RunLoop loop;
-    HeadlessBackend backend { test::sharedDisplay() };
+    HeadlessBackend backend;
     BackendScope scope { backend };
     OffscreenView view { backend.getContext() };
     StubFileSource fileSource;