More mypy fixes

Author: dstansby

numcodecs/tests/test_entrypoints_backport.py

@@ -1,4 +1,4 @@
-import importlib
+import importlib.util
 import os.path
 import sys
 from multiprocessing import Process
@@ -7,7 +7,8 @@
 
 import numcodecs.registry
 
-if not importlib.util.find_spec("importlib_metadata").loader:  # pragma: no cover
+importlib_spec = importlib.util.find_spec("importlib_metadata")
+if importlib_spec is None or not importlib_spec.loader:  # pragma: no cover
     pytest.skip(
         "This test module requires importlib_metadata to be installed",
         allow_module_level=True,

pyproject.toml

@@ -175,3 +175,7 @@ quote-style = "preserve"
 [tool.mypy]
 ignore_errors = false
 ignore_missing_imports = true
+enable_error_code = ["ignore-without-code", "redundant-expr", "truthy-bool"]
+# TODO: set options below to true
+strict = false
+warn_unreachable = false