[CI] Ignore existing DLLs in Windows wheel repair (#635)

Windows wheel repair started failing under the current
cibuildwheel/delvewheel stack with:

```text
FileNotFoundError: Unable to find library: tvm_ffi_testing.dll
```

`tvm_ffi_testing.dll` is already shipped inside the wheel under
`tvm_ffi/lib/`. Configure the Windows repair command to pass
`--ignore-existing`, so delvewheel does not try to rediscover DLLs that
are already bundled in the wheel while repairing `tvm_ffi/core*.pyd`.

Validation:

- Manually triggered Windows wheel workflow on `tqchen/tvm-ffi:main`
passed with this change.
- `pre-commit run --all-files` passed locally.

Author: tqchen

pyproject.toml

@@ -253,6 +253,7 @@ environment = { MACOSX_DEPLOYMENT_TARGET = "10.14" }
 
 [tool.cibuildwheel.windows]
 archs = ["AMD64"]
+repair-wheel-command = "delvewheel repair --ignore-existing -w {dest_dir} -v {wheel}"
 
 [tool.ty.environment]
 python-version = "3.9"