Add ninja as dev dependency (#127380)

`ninja` is required to build C++ extensions in tests.

```pytb
ERROR: test_autograd_cpp_node (__main__.TestCompiledAutograd)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/PanXuehai/Projects/pytorch/torch/testing/_internal/common_utils.py", line 2741, in wrapper
    method(*args, **kwargs)
  File "test/inductor/test_compiled_autograd.py", line 1061, in test_autograd_cpp_node
    module = torch.utils.cpp_extension.load_inline(
  File "/home/PanXuehai/Projects/pytorch/torch/utils/cpp_extension.py", line 1643, in load_inline
    return _jit_compile(
  File "/home/PanXuehai/Projects/pytorch/torch/utils/cpp_extension.py", line 1718, in _jit_compile
    _write_ninja_file_and_build_library(
  File "/home/PanXuehai/Projects/pytorch/torch/utils/cpp_extension.py", line 1800, in _write_ninja_file_and_build_library
    verify_ninja_availability()
  File "/home/PanXuehai/Projects/pytorch/torch/utils/cpp_extension.py", line 1849, in verify_ninja_availability
    raise RuntimeError("Ninja is required to load C++ extensions")
RuntimeError: Ninja is required to load C++ extensions

To execute this test, run the following from the base repo dir:
     python test/inductor/test_compiled_autograd.py -k TestCompiledAutograd.test_autograd_cpp_node
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/127380
Approved by: https://github.com/ezyang

requirements.txt

@@ -15,6 +15,7 @@ networkx
 jinja2
 fsspec
 lintrunner
+ninja
 # setuptools was removed from default python install
 setuptools ; python_version >= "3.12"
 packaging