Fix Config.from_file silent error handling to include ENOTDIR

Config.from_file() was missing errno.ENOTDIR in its silent error
handling, while Config.from_pyfile() correctly includes it.

When a component of the config file path is a regular file rather
than a directory (e.g., trying to load 'file/config.json' where
'file' is a regular file), from_file(silent=True) would raise an
OSError instead of silently returning False.

This adds ENOTDIR to match from_pyfile's behavior and adds a test
to verify the fix.

Fixes #5912

src/flask/config.py

@@ -293,7 +293,7 @@ class Config(dict):  # type: ignore[type-arg]
             with open(filename, "r" if text else "rb") as f:
                 obj = load(f)
         except OSError as e:
-            if silent and e.errno in (errno.ENOENT, errno.EISDIR):
+            if silent and e.errno in (errno.ENOENT, errno.EISDIR, errno.ENOTDIR):
                 return False
 
             e.strerror = f"Unable to load configuration file ({e.strerror})"

tests/test_config.py

@@ -195,6 +195,19 @@ def test_config_missing_file():
     assert not app.config.from_file("missing.json", load=json.load, silent=True)
 
 
+def test_config_from_file_not_a_directory(tmp_path):
+    """from_file with silent=True returns False when a path component is not a
+    directory, matching the behavior of from_pyfile."""
+    file_in_tmp = tmp_path / "not_a_dir"
+    file_in_tmp.write_text("{}")
+    app = flask.Flask(__name__)
+    app.config.root_path = str(tmp_path)
+    # not_a_dir/config.json: not_a_dir is a file, not a directory
+    assert not app.config.from_file(
+        "not_a_dir/config.json", load=json.load, silent=True
+    )
+
+
 def test_custom_config_class():
     class Config(flask.Config):
         pass