don't force this dependency; tibs is a new beta-test project and isn't
actually required at runtime (currently can be used if an env var is
set while running)

Index: pyproject.toml
--- pyproject.toml.orig
+++ pyproject.toml
@@ -30,7 +30,6 @@ classifiers = [
 keywords = ["binary", "bitarray", "bitvector", "bitfield"]
 dependencies = [
   "bitarray >= 3.0.0, < 4.0",
-  "tibs >= 0.5.6, < 0.6",
 ]
 
 [project.urls]
