Fix data race in cometbft server OE

[julienrbrt]

ref: https://github.com/cosmos/cosmos-sdk/actions/runs/12352402806/job/34469368664?pr=22885

==================
WARNING: DATA RACE
Read at 0x00c000a683a0 by goroutine 384:
  encoding/hex.Encode()
      /opt/hostedtoolcache/go/1.23.4/x64/src/encoding/hex/hex.go:47 +0xa9
  encoding/hex.EncodeToString()
      /opt/hostedtoolcache/go/1.23.4/x64/src/encoding/hex/hex.go:128 +0x4a
  cosmossdk.io/server/v2/cometbft/oe.(*OptimisticExecution[go.shape.struct { Sender []uint8; Msg interface { ProtoMessage(); Reset(); String() string }; GasLimit uint64 }]).Execute.func1()
      /home/runner/work/cosmos-sdk/cosmos-sdk/server/v2/cometbft/oe/optimistic_execution.go:118 +0x1c8

Previous write at 0x00c000a683a0 by goroutine 367:
  cosmossdk.io/server/v2/cometbft.TestOptimisticExecution()
      /home/runner/work/cosmos-sdk/cosmos-sdk/server/v2/cometbft/abci_test.go:962 +0xa74
  testing.tRunner()
      /opt/hostedtoolcache/go/1.23.4/x64/src/testing/testing.go:1690 +0x226
  testing.(*T).Run.gowrap1()
      /opt/hostedtoolcache/go/1.23.4/x64/src/testing/testing.go:1743 +0x44

Goroutine 384 (running) created at:
  cosmossdk.io/server/v2/cometbft/oe.(*OptimisticExecution[go.shape.struct { Sender []uint8; Msg interface { ProtoMessage(); Reset(); String() string }; GasLimit uint64 }]).Execute()
      /home/runner/work/cosmos-sdk/cosmos-sdk/server/v2/cometbft/oe/optimistic_execution.go:111 +0xb8b
  cosmossdk.io/server/v2/cometbft.(*consensus[go.shape.struct { Sender []uint8; Msg interface { ProtoMessage(); Reset(); String() string }; GasLimit uint64 }]).ProcessProposal()
      /home/runner/work/cosmos-sdk/cosmos-sdk/server/v2/cometbft/abci.go:452 +0xe50
  cosmossdk.io/server/v2/cometbft.TestOptimisticExecution()
      /home/runner/work/cosmos-sdk/cosmos-sdk/server/v2/cometbft/abci_test.go:957 +0x98d
  testing.tRunner()
      /opt/hostedtoolcache/go/1.23.4/x64/src/testing/testing.go:1690 +0x226
  testing.(*T).Run.gowrap1()
      /opt/hostedtoolcache/go/1.23.4/x64/src/testing/testing.go:1743 +0x44

Goroutine 367 (running) created at:
  testing.(*T).Run()
      /opt/hostedtoolcache/go/1.23.4/x64/src/testing/testing.go:1743 +0x825
  testing.runTests.func1()
      /opt/hostedtoolcache/go/1.23.4/x64/src/testing/testing.go:2168 +0x85
  testing.tRunner()
      /opt/hostedtoolcache/go/1.23.4/x64/src/testing/testing.go:1690 +0x226
  testing.runTests()
      /opt/hostedtoolcache/go/1.23.4/x64/src/testing/testing.go:2166 +0x8be
  testing.(*M).Run()
      /opt/hostedtoolcache/go/1.23.4/x64/src/testing/testing.go:2034 +0xf17
  main.main()
      _testmain.go:83 +0x[164](https://github.com/cosmos/cosmos-sdk/actions/runs/12352402806/job/34469368664?pr=22885#step:5:165)
==================
--- FAIL: TestOptimisticExecution (0.00s)
    testing.go:1399: race detected during execution of test
FAIL
exit status 1
FAIL	cosmossdk.io/server/v2/cometbft	0.349s