Rewrite a useless std::memory_order_release as std::memory_order_relaxed.

It's OK because these stores happen before calling Execute, and these values
will only be consumed in other threads after Execute has communicated with
these threads... which will involve a release-store anyway.

This might matter because this suggests that at least on ARM32, each release-store may involve a __sync_synchronize and the compiler may not know to keep only the last memory barrier in a loop that only performs stores:
https://godbolt.org/z/HYijeI

PiperOrigin-RevId: 259982740

tensorflow/lite/experimental/ruy/trmul.cc

@@ -237,7 +237,7 @@ void TrMul(TrMulParams* params, Context* context) {
       const int size = NumBlocksPerSide(side, block_map);
       allocator->Allocate(size, &packed[side]);
       for (int i = 0; i < size; i++) {
-        packed[side][i].store(false, std::memory_order_release);
+        packed[side][i].store(false, std::memory_order_relaxed);
       }
     }
   }