Add more clarifying comment

Author: maximdimakov

sycl/unittests/kernel-and-program/MultipleDevsCache.cpp

@@ -211,8 +211,11 @@ TEST_F(MultipleDeviceCacheTest, ProgramRetain) {
 
     EXPECT_EQ(KernelCache.size(), (size_t)2) << "Expect 2 kernels in cache";
   }
-  // Cache is cleared here, check kernel release
-  // 3 kernel releases is expected because kernel_bundle::get_kernel() calls
-  // piKernelRetain so one more kernel release is needed
+  // First kernel creating is called in handler::single_task().
+  // kernel_bundle::get_kernel() creates a kernel and shares it with created programs.
+  // Also the kernel is retained in kernel_bundle::get_kernel().
+  // A kernel is removed from cache if piKernelRelease was called for it,
+  // so it will not be removed twice for the other programs.
+  // As a result we must expect 3 piKernelRelease calls.
   EXPECT_EQ(KernelReleaseCounter, 3) << "Expect 3 piKernelRelease calls";
 }