Fix crash with report generation on namespace packages (#13733)

Fixes #11234

Author: hauntsaninja

mypy/report.py

@@ -140,8 +140,12 @@ def should_skip_path(path: str) -> bool:
 
 def iterate_python_lines(path: str) -> Iterator[tuple[int, str]]:
     """Return an iterator over (line number, line text) from a Python file."""
-    with tokenize.open(path) as input_file:
-        yield from enumerate(input_file, 1)
+    try:
+        with tokenize.open(path) as input_file:
+            yield from enumerate(input_file, 1)
+    except IsADirectoryError:
+        # can happen with namespace packages
+        pass
 
 
 class FuncCounterVisitor(TraverserVisitor):