Bumps [github.com/decred/dcrd/dcrec/secp256k1/v4](https://github.com/decred/dcrd) from 4.1.0 to 4.2.0.
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<summary>Commits</summary>
<ul>
<li><a href="bacf8444a8"><code>bacf844</code></a> secp256k1: Prepare v4.2.0.</li>
<li><a href="e0ad9b8687"><code>e0ad9b8</code></a> secp256k1: Update PrivKeyFromBytes comment.</li>
<li><a href="6c5b953d28"><code>6c5b953</code></a> secp256k1: Add GeneratePrivateKeyFromRand tests.</li>
<li><a href="bd0b82d0be"><code>bd0b82d</code></a> secp256k1: Require concerete rand for privkey gen.</li>
<li><a href="b4fab9efd8"><code>b4fab9e</code></a> chaincfg/chainhash: Prepare v1.0.4.</li>
<li><a href="d71616bddb"><code>d71616b</code></a> secp256k1: Add GeneratePrivateKeyFromRand function</li>
<li><a href="9aa79ec168"><code>9aa79ec</code></a> chaincfg: Introduce subsidy split change r2 agenda.</li>
<li><a href="7db7325c42"><code>7db7325</code></a> chaincfg: Introduce BLAKE3 PoW agenda.</li>
<li><a href="ce46220cf7"><code>ce46220</code></a> secp256k1: Fix typo in a doc comment</li>
<li><a href="ca02bcaf5a"><code>ca02bca</code></a> docs: Add release notes for v1.7.7.</li>
<li>Additional commits viewable in <a href="https://github.com/decred/dcrd/compare/blockchain/v4.1.0...dcrec/secp256k1/v4.2.0">compare view</a></li>
</ul>
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