Pin Onnx Version (#20073)

### Description
1. change in build.py is to fix DML exception
(https://dev.azure.com/onnxruntime/onnxruntime/_build?definitionId=10&_a=summary)
2. change in requirements.txt is to fix exception in python packaging
pipeline.
https://dev.azure.com/aiinfra/Lotus/_build/results?buildId=430433&view=results



### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->

---------

Co-authored-by: Yi Zhang <your@email.com>

onnxruntime/test/python/requirements.txt

@@ -1,2 +1,2 @@
-onnx
-pytest
+onnx==1.15.0
+pytest

tools/ci_build/build.py

@@ -2087,7 +2087,9 @@ def run_onnxruntime_tests(args, source_dir, ctest_path, build_dir, configs):
                     run_subprocess(
                         [sys.executable, "-m", "pip", "uninstall", "--yes", "onnx"], cwd=cwd, dll_path=dll_path
                     )
-                    run_subprocess([sys.executable, "-m", "pip", "install", "-q", "onnx"], cwd=cwd, dll_path=dll_path)
+                    run_subprocess(
+                        [sys.executable, "-m", "pip", "install", "-q", "onnx==1.15.0"], cwd=cwd, dll_path=dll_path
+                    )
                 run_subprocess([sys.executable, "onnxruntime_test_python_iobinding.py"], cwd=cwd, dll_path=dll_path)
 
             if args.use_cuda: