Fix missing include for CudaHasBF16Support in conv_fp16_test.cc (microsoft#26671)

### Description

Adds missing `#include "test/common/cuda_op_test_utils.h"` to
`conv_fp16_test.cc`.

The `ConvBF16Test_Conv2D_1` test calls `CudaHasBF16Support()` but the
header defining it was not included.

### Motivation and Context

Fixes Linux CPU packaging pipeline build failure:

```
/onnxruntime_src/onnxruntime/test/providers/cpu/nn/conv_fp16_test.cc:281:8: error: 'CudaHasBF16Support' was not declared in this scope
  281 |   if (!CudaHasBF16Support()) {
      |        ^~~~~~~~~~~~~~~~~~
```

Other test files using this function (`pool_fp16_op_test.cc`,
`element_wise_ops_test.cc`, `skiplayernorm_op_test.cc`) already include
this header.

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<details>

<summary>Original prompt</summary>

> Linux CPU packaging pipeline failed with this error:
> 
> 
> ```
> /onnxruntime_src/onnxruntime/test/providers/cpu/nn/conv_fp16_test.cc:
In member function ‘virtual void
onnxruntime::test::ConvBF16Test_Conv2D_1_Test::TestBody()’:
>
/onnxruntime_src/onnxruntime/test/providers/cpu/nn/conv_fp16_test.cc:281:8:
error: ‘CudaHasBF16Support’ was not declared in this scope
>   281 |   if (!CudaHasBF16Support()) {
>       |        ^~~~~~~~~~~~~~~~~~
> ```
> 
> it looks like `CudaHasBF16Support` is declared inside a macro section
which is inconsistent.
> 
> Please try to figure out the reason and perform a fix and make a PR
for it


</details>



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Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: fs-eire <[email protected]>

Author: Copilot

onnxruntime/test/providers/cpu/nn/conv_fp16_test.cc

@@ -6,6 +6,7 @@
 #if defined(MLAS_F16VEC_INTRINSICS_SUPPORTED) || defined(USE_COREML) || defined(USE_XNNPACK) || defined(USE_WEBGPU)
 
 #include "gtest/gtest.h"
+#include "test/common/cuda_op_test_utils.h"
 #include "test/common/random_generator.h"
 #include "test/providers/provider_test_utils.h"
 #include "default_providers.h"