Fix ImportError crash when using --import-mode=importlib (#13053) (#13054)

Regression in #12716

In short: `PathFinder.find_spec` received the argument `/cow/moo` but loaded `/cow/moo/moo.py` instead.

**Trigger conditions:**
1. `/cow/moo/moo.py` exists (a file and directory with the same name).
2. `/cow/moo/test_moo.py` exists (test case resides in the directory).

When pytest loads test files in `importlib` mode, it continues recursive loading upward:
- When loading `cow.moo`, it should return a namespace but unexpectedly returns a module.
- When loading `cow.moo.moo`, it should return a module but unexpectedly returns a namespace.

**Complete example:** [[GitHub repository](https://github.com/dongfangtianyu/pytest_importlib_issue)](https://github.com/dongfangtianyu/pytest_importlib_issue)
- `main.py`: Reproduces the error.
- `debug.py`: Demonstrates the behavior of `PathFinder.find_spec`.

**Context:**
#12592 (comment)
#12592 (comment)

---------

Co-authored-by: Bruno Oliveira <bruno@soliv.dev>
(cherry picked from commit 28e1e25)

Co-authored-by: dongfangtianyu <7629022+dongfangtianyu@users.noreply.github.com>

Author: patchback[bot]

changelog/13053.bugfix.rst

@@ -0,0 +1 @@
+Fixed a regression in pytest 8.3.4 where, when using ``--import-mode=importlib``, a directory containing py file with the same name would cause an ``ImportError``

src/_pytest/pathlib.py

@@ -694,9 +694,16 @@ def _import_module_using_spec(
     # Checking with sys.meta_path first in case one of its hooks can import this module,
     # such as our own assertion-rewrite hook.
     for meta_importer in sys.meta_path:
-        spec = meta_importer.find_spec(
-            module_name, [str(module_location), str(module_path)]
-        )
+        module_name_of_meta = getattr(meta_importer.__class__, "__module__", "")
+        if module_name_of_meta == "_pytest.assertion.rewrite" and module_path.is_file():
+            # Import modules in subdirectories by module_path
+            # to ensure assertion rewrites are not missed (#12659).
+            find_spec_path = [str(module_location), str(module_path)]
+        else:
+            find_spec_path = [str(module_location)]
+
+        spec = meta_importer.find_spec(module_name, find_spec_path)
+
         if spec_matches_module_path(spec, module_path):
             break
     else:

testing/test_pathlib.py

@@ -1498,6 +1498,34 @@ def test():
             ]
         )
 
+    def test_ns_multiple_levels_import_error(
+        self,
+        tmp_path: Path,
+        pytester: Pytester,
+    ) -> None:
+        # Trigger condition 1: ns and file with the same name
+        file = pytester.path / "cow/moo/moo.py"
+        file.parent.mkdir(parents=True)
+        file.write_text("data=123", encoding="utf-8")
+
+        # Trigger condition 2: tests are located in ns
+        tests = pytester.path / "cow/moo/test_moo.py"
+
+        tests.write_text(
+            dedent(
+                """
+            from cow.moo.moo import data
+
+            def test_moo():
+                print(data)
+            """
+            ),
+            encoding="utf-8",
+        )
+
+        result = pytester.runpytest("--import-mode=importlib")
+        assert result.ret == ExitCode.OK
+
     @pytest.mark.parametrize("import_mode", ["prepend", "append", "importlib"])
     def test_incorrect_namespace_package(
         self,