Bump protobuf from 3.20.2 to 6.33.5 in /tools/sdg (#5950)

Bumps [protobuf](https://github.com/protocolbuffers/protobuf) from
3.20.2 to 6.33.5.
<details>
<summary>Release notes</summary>
<p><em>Sourced from <a
href="https://github.com/protocolbuffers/protobuf/releases">protobuf's
releases</a>.</em></p>
<blockquote>
<h2>Protocol Buffers v3.20.3</h2>
<h1>Java</h1>
<ul>
<li>Refactoring java full runtime to reuse sub-message builders and
prepare to
migrate parsing logic from parse constructor to builder.</li>
<li>Move proto wireformat parsing functionality from the private
&quot;parsing
constructor&quot; to the Builder class.</li>
<li>Change the Lite runtime to prefer merging from the wireformat into
mutable
messages rather than building up a new immutable object before merging.
This
way results in fewer allocations and copy operations.</li>
<li>Make message-type extensions merge from wire-format instead of
building up
instances and merging afterwards. This has much better performance.</li>
<li>Fix TextFormat parser to build up recurring (but supposedly not
repeated)
sub-messages directly from text rather than building a new sub-message
and
merging the fully formed message into the existing field.</li>
<li>This release addresses a <a
href="https://github.com/protocolbuffers/protobuf/security/advisories/GHSA-h4h5-3hr4-j3g2">Security
Advisory for Java users</a></li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li>See full diff in <a
href="https://github.com/protocolbuffers/protobuf/commits">compare
view</a></li>
</ul>
</details>
<br />


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tools/sdg/requirements.txt

@@ -1 +1 @@
-protobuf==3.20.2
+protobuf==5.29.6