Update protobuf requirement from <6,>=4.21.6 to >=4.21.6,<7 (#129)

Updates the requirements on
[protobuf](https://github.com/protocolbuffers/protobuf) to permit the
latest version.
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/protocolbuffers/protobuf/commit/0d815c5b74281f081c1ee4b431a4d5bbb1615c97"><code>0d815c5</code></a>
Updating version.json and repo version numbers to: 30.1</li>
<li><a
href="https://github.com/protocolbuffers/protobuf/commit/ebb5224493150126861ce2e192d7ae244bfea1df"><code>ebb5224</code></a>
Re-add <code>system_python</code> repo alias to MODULE.bazel (<a
href="https://redirect.github.com/protocolbuffers/protobuf/issues/20662">#20662</a>)</li>
<li><a
href="https://github.com/protocolbuffers/protobuf/commit/4747628cce300d58e3bb0da4f3ee7cbfa1ac853b"><code>4747628</code></a>
Remove Java runtime classes from kotlin release. (<a
href="https://redirect.github.com/protocolbuffers/protobuf/issues/20607">#20607</a>)</li>
<li><a
href="https://github.com/protocolbuffers/protobuf/commit/250c5502fa436e82fca50937db7d28f43855b09e"><code>250c550</code></a>
Fix python codegen crash when C++ features are used. (<a
href="https://redirect.github.com/protocolbuffers/protobuf/issues/20577">#20577</a>)</li>
<li><a
href="https://github.com/protocolbuffers/protobuf/commit/3576a1f8732c4a42df90e406e07326198182b6fb"><code>3576a1f</code></a>
Loosen py_proto_library check to be on the import path instead of full
direct...</li>
<li><a
href="https://github.com/protocolbuffers/protobuf/commit/efa65c59858cd83f348628a3c5cb350082f3199a"><code>efa65c5</code></a>
Merge pull request <a
href="https://redirect.github.com/protocolbuffers/protobuf/issues/20562">#20562</a>
from protocolbuffers/30.x-202503042254</li>
<li><a
href="https://github.com/protocolbuffers/protobuf/commit/63fc9d680507ceb41d4acbf17b138e4f6f85f86b"><code>63fc9d6</code></a>
Updating version.json and repo version numbers to: 30.1-dev</li>
<li><a
href="https://github.com/protocolbuffers/protobuf/commit/d295af5c3002c08e1bfd9d7f9e175d0a4d015f1e"><code>d295af5</code></a>
Updating version.json and repo version numbers to: 30.0</li>
<li><a
href="https://github.com/protocolbuffers/protobuf/commit/a5c906a6e70d9efbc82651e0ea88480545fb0105"><code>a5c906a</code></a>
Split maven dependencies into dev vs local (<a
href="https://redirect.github.com/protocolbuffers/protobuf/issues/20549">#20549</a>)
(<a
href="https://redirect.github.com/protocolbuffers/protobuf/issues/20558">#20558</a>)</li>
<li><a
href="https://github.com/protocolbuffers/protobuf/commit/6059cb7bb921c7d8a84c0ada2dfa68f1fe7492bc"><code>6059cb7</code></a>
Cherry-pick notices change for 30.x</li>
<li>Additional commits viewable in <a
href="https://github.com/protocolbuffers/protobuf/compare/v4.22.0-rc1...v6.30.1">compare
view</a></li>
</ul>
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Author: llucax

pyproject.toml

@@ -40,7 +40,7 @@ dependencies = [
   "frequenz-channels >= 1.0.0-rc1, < 2.0.0",
   "frequenz-client-base >= 0.8.0, < 0.10.0",
   "grpcio >= 1.54.2, < 2",
-  "protobuf >= 4.21.6, < 6",
+  "protobuf >= 4.21.6, < 7",
   "timezonefinder >= 6.2.0, < 7",
   "typing-extensions >= 4.5.0, < 5",
 ]