fix: p256 flaky test

[songgaoye]

Description

The pull request references are PR #332 and PR #274.

I believe PR #274 also requires a modification in another location.

evm/tests/integration/precompiles/p256/test_p256.go

Lines 63 to 69 in cffad65

	rBz, sBz, err := parseSignature(sig)
	s.Require().NoError(err)
	input := make([]byte, p256.VerifyInputLength)
	copy(input[0:32], hash)
	copy(input[32:64], rBz)
	copy(input[64:96], sBz)

Referring to issue #273, I think rBz, rBz(when shorter than 32 bytes) has the same issue.

Closes: #XXXX

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