Resolve a TypeError lurking in the read_text() functional API

`importlib_resources.read_text()` calls the `Traversable.read_text()`
concrete method with an `errors` argument that doesn't exist in the
method signature, resulting in an `TypeError`.

This is resolved by adding an `errors` parameter to
`Traversable.read_text()`.

Fixes python/cpython#127012

importlib_resources/abc.py

@@ -80,11 +80,13 @@ def read_bytes(self) -> bytes:
         with self.open('rb') as strm:
             return strm.read()
 
-    def read_text(self, encoding: Optional[str] = None) -> str:
+    def read_text(
+        self, encoding: Optional[str] = None, errors: Optional[str] = None
+    ) -> str:
         """
         Read contents of self as text
         """
-        with self.open(encoding=encoding) as strm:
+        with self.open(encoding=encoding, errors=errors) as strm:
             return strm.read()
 
     @abc.abstractmethod