fixup: Config.cache cannot be None

Author: RonnyPfannschmidt

src/_pytest/config/__init__.py

@@ -1024,7 +1024,7 @@ class ArgsSource(enum.Enum):
         TESTPATHS = enum.auto()
 
     # Set by cacheprovider plugin.
-    cache: Cache | None
+    cache: Cache
 
     def __init__(
         self,