Skip the Muse Glimmer workload compile test on Windows (#24017)

### Problem

All four Windows unit test jobs (`unittest`, `unittest-editable` and
`unittest-release`, in `pull` and `trunk`) fail on `main` because of one
test:

```
FAILED .ci/scripts/tests/test_muse_glimmer_batching_workload.py::MuseGlimmerBatchingWorkloadTest::test_workload_without_a_model
AssertionError: unexpectedly None : CI workload tests require a C++ compiler
=== 1 failed, 1998 passed, 82 skipped, 14 deselected ===
```

The test builds a small C++ program by running the `c++` command with
GCC and Clang flags (`-std=c++17 -pthread -Werror ...`). Windows runners
have no `c++` command, so the test fails at its first check. The test
was added recently, and the Windows jobs were green on the commit before
it.

### Fix

Skip this one test on Windows. Other tests in `.ci/scripts/tests`
already do this when they need Unix-only tools, for example
`test_pybind_cmake.py`.

On Linux and macOS nothing changes. The test still requires the compiler
and still fails when it is missing. The CUDA job that this test was
written for runs on Linux, so it keeps full coverage there.

### Testing

- On macOS the test still builds and runs the C++ program and passes.
- With `sys.platform` set to `win32` the test is skipped.
- On macOS with no `c++` on `PATH` the test still fails with the same
assertion, so the check is not weakened.

Author: shoumikhin

.ci/scripts/tests/test_muse_glimmer_batching_workload.py

@@ -7,6 +7,7 @@
 import os
 import shutil
 import subprocess
+import sys
 import tempfile
 import unittest
 from pathlib import Path
@@ -16,6 +17,9 @@
 
 
 class MuseGlimmerBatchingWorkloadTest(unittest.TestCase):
+    @unittest.skipIf(
+        sys.platform == "win32", "Builds with a GCC or Clang style c++ driver"
+    )
     def test_workload_without_a_model(self):
         compiler = shutil.which("c++")
         self.assertIsNotNone(compiler, "CI workload tests require a C++ compiler")