build(deps): bump protobuf from 3.20.1 to 3.20.2 in /.kokoro (#1465)

Bumps [protobuf](https://togithub.com/protocolbuffers/protobuf) from 3.20.1 to 3.20.2.
<details>
<summary>Release notes</summary>
<p><em>Sourced from <a href="https://togithub.com/protocolbuffers/protobuf/releases">protobuf's releases</a>.</em></p>
<blockquote>
<h2>Protocol Buffers v3.20.2</h2>
<h1>C++</h1>
<ul>
<li>Reduce memory consumption of MessageSet parsing</li>
<li>This release addresses a <a href="https://togithub.com/protocolbuffers/protobuf/security/advisories/GHSA-8gq9-2x98-w8hf">Security Advisory for C++ and Python users</a></li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a href="https://togithub.com/protocolbuffers/protobuf/commit/a20c65f2cd549445fda907f7b83894c8eb7427d6"><code>a20c65f</code></a> Updating changelog</li>
<li><a href="https://togithub.com/protocolbuffers/protobuf/commit/c49fe79af9c295960477b7568f1765b202093143"><code>c49fe79</code></a> Updating version.json and repo version numbers to: 20.2</li>
<li><a href="https://togithub.com/protocolbuffers/protobuf/commit/806d7e4ce6f1fd0545cae226b94cb0249ea495c7"><code>806d7e4</code></a> Merge pull request <a href="https://github-redirect.dependabot.com/protocolbuffers/protobuf/issues/10544">#10544</a> from deannagarcia/3.20.x</li>
<li><a href="https://togithub.com/protocolbuffers/protobuf/commit/ae718b39020ae6e6f8f5568e357d6893fd0fd29c"><code>ae718b3</code></a> Add missing includes</li>
<li><a href="https://togithub.com/protocolbuffers/protobuf/commit/b4c395aaedfacb32e2414d361fa85968c0991b34"><code>b4c395a</code></a> Apply patch</li>
<li><a href="https://togithub.com/protocolbuffers/protobuf/commit/6439c5c01349e74d4deb57c844a7ad4b7b13a302"><code>6439c5c</code></a> Merge pull request <a href="https://github-redirect.dependabot.com/protocolbuffers/protobuf/issues/10531">#10531</a> from protocolbuffers/deannagarcia-patch-7</li>
<li><a href="https://togithub.com/protocolbuffers/protobuf/commit/22c79e6e4ca8be2bc2f700b2cdddca84d84659ce"><code>22c79e6</code></a> Update version.json</li>
<li><a href="https://togithub.com/protocolbuffers/protobuf/commit/c1a2d2ec29314975e725021ffe4334926dbaa56c"><code>c1a2d2e</code></a> Fix python release on macos (<a href="https://github-redirect.dependabot.com/protocolbuffers/protobuf/issues/10512">#10512</a>)</li>
<li><a href="https://togithub.com/protocolbuffers/protobuf/commit/a826282e15efe3ae3a2aebb040fb1691b2233a1e"><code>a826282</code></a> Merge pull request <a href="https://github-redirect.dependabot.com/protocolbuffers/protobuf/issues/10505">#10505</a> from deannagarcia/3.20.x</li>
<li><a href="https://togithub.com/protocolbuffers/protobuf/commit/7639a710e10beb47bfc62f363680f7b04e8b3d26"><code>7639a71</code></a> Add version file</li>
<li>Additional commits viewable in <a href="https://togithub.com/protocolbuffers/protobuf/compare/v3.20.1...v3.20.2">compare view</a></li>
</ul>
</details>
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