[mlir] Fix windows build bot break due to use of `alloca` in a test.

[stella.stamenova]

LGTM.

mlir/test/CAPI/sparse_tensor.c

MlirAffineMap dimOrdering =
       mlirSparseTensorEncodingAttrGetDimOrdering(originalAttr);
   // CHECK: (d0, d1, d2) -> (d0, d1, d2)
   mlirAffineMapDump(dimOrdering);
   // CHECK: level_type: 0
   // CHECK: level_type: 1
   // CHECK: level_type: 2
   int numLevelTypes = mlirSparseTensorEncodingGetNumDimLevelTypes(originalAttr);
   enum MlirSparseTensorDimLevelType *levelTypes =
-      alloca(sizeof(enum MlirSparseTensorDimLevelType) * numLevelTypes);
+      malloc(sizeof(enum MlirSparseTensorDimLevelType) * numLevelTypes);
   for (int i = 0; i < numLevelTypes; ++i) {
     levelTypes[i] =
         mlirSparseTensorEncodingAttrGetDimLevelType(originalAttr, i);
     fprintf(stderr, "level_type: %d\n", levelTypes[i]);
   }
   // CHECK: pointer: 32
   int pointerBitWidth =
       mlirSparseTensorEncodingAttrGetPointerBitWidth(originalAttr);
   fprintf(stderr, "pointer: %d\n", pointerBitWidth);
   // CHECK: index: 64
   int indexBitWidth =
       mlirSparseTensorEncodingAttrGetIndexBitWidth(originalAttr);
   fprintf(stderr, "index: %d\n", indexBitWidth);
 
   MlirAttribute newAttr = mlirSparseTensorEncodingAttrGet(
       ctx, numLevelTypes, levelTypes, dimOrdering, pointerBitWidth,
       indexBitWidth);
   mlirAttributeDump(newAttr); // For debugging filecheck output.
   // CHECK: equal: 1
   fprintf(stderr, "equal: %d\n", mlirAttributeEqual(originalAttr, newAttr));
+
+  free(levelTypes);
   return 0;
 }
 
 int main() {
   MlirContext ctx = mlirContextCreate();
   mlirDialectHandleRegisterDialect(mlirGetDialectHandle__sparse_tensor__(),
                                    ctx);
   if (testRoundtripEncoding(ctx))
     return 1;
 
   mlirContextDestroy(ctx);
   return 0;
 }