Fix sanity check shell: use cmd to avoid MSYS path mangling

Git Bash on Windows converts /nologo and /EHsc to filesystem paths
(C:/Program Files/Git/nologo etc.). Switch the sanity check step to
cmd shell so MSVC flags are passed verbatim.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: AntoinePrv

.github/workflows/windows.yml

@@ -20,19 +20,18 @@ jobs:
     - name: Checkout xsimd
       uses: actions/checkout@v6
     - name: Sanity check NEON intrinsics
+      shell: cmd
       run: |
-        cat > sanity_neon.cpp << 'EOF'
-        #include <arm_neon.h>
-        int main() {
-            uint8x16_t a = vdupq_n_u8(1);
-            uint8x16_t b = vdupq_n_u8(2);
-            uint8x16_t c = vaddq_u8(a, b);
-            (void)c;
-            return 0;
-        }
-        EOF
+        echo #include ^<arm_neon.h^> > sanity_neon.cpp
+        echo int main() { >> sanity_neon.cpp
+        echo     uint8x16_t a = vdupq_n_u8(1); >> sanity_neon.cpp
+        echo     uint8x16_t b = vdupq_n_u8(2); >> sanity_neon.cpp
+        echo     uint8x16_t c = vaddq_u8(a, b); >> sanity_neon.cpp
+        echo     (void)c; >> sanity_neon.cpp
+        echo     return 0; >> sanity_neon.cpp
+        echo } >> sanity_neon.cpp
         cl /nologo /EHsc sanity_neon.cpp /Fe:sanity_neon.exe
-        ./sanity_neon.exe
+        sanity_neon.exe
     - name: Setup
       run: cmake -B _build -DBUILD_TESTS=ON -DDOWNLOAD_DOCTEST=ON -DBUILD_BENCHMARK=ON -DBUILD_EXAMPLES=ON -DCMAKE_BUILD_TYPE=Release -G Ninja
     - name: Build