trie: fix benchmark by ensuring key immutability (ethereum#28221)

This change fixes the bug in a benchmark, where the input to the trie is reused in a way which is not correct. 

---------

Co-authored-by: Martin Holst Swende <martin@swende.se>

trie/trie_test.go

@@ -614,7 +614,9 @@ func benchGet(b *testing.B) {
  k := make([]byte, 32)
  for i := 0; i < benchElemCount; i++ {
  binary.LittleEndian.PutUint64(k, uint64(i))
- trie.MustUpdate(k, k)
+ v := make([]byte, 32)
+ binary.LittleEndian.PutUint64(v, uint64(i))
+ trie.MustUpdate(k, v)
  }
  binary.LittleEndian.PutUint64(k, benchElemCount/2)
 
@@ -630,8 +632,10 @@ func benchUpdate(b *testing.B, e binary.ByteOrder) *Trie {
  k := make([]byte, 32)
  b.ReportAllocs()
  for i := 0; i < b.N; i++ {
+ v := make([]byte, 32)
  e.PutUint64(k, uint64(i))
- trie.MustUpdate(k, k)
+ e.PutUint64(v, uint64(i))
+ trie.MustUpdate(k, v)
  }
  return trie
 }