Exclude test_annotations from pypy3

See #509
diff --git a/conftest.py b/conftest.py
index 9f84c34..cce4950 100644
--- a/conftest.py
+++ b/conftest.py
@@ -6,6 +6,8 @@
 
 from hypothesis import HealthCheck, settings
 
+from attr._compat import PYPY
+
 
 def pytest_configure(config):
     # HealthCheck.too_slow causes more trouble than good -- especially in CIs.
@@ -35,3 +37,5 @@
     collect_ignore.extend(
         ["tests/test_annotations.py", "tests/test_init_subclass.py"]
     )
+elif PYPY:  # FIXME: Currently our tests fail on pypy3. See #509
+    collect_ignore.extend(["tests/test_annotations.py"])