Update protobuf requirement from <5,>=4.21.6 to >=4.21.6,<6 (#936)

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/2434ef2adf0c74149b9d547ac5fb545a1ff8b6b5"><code>2434ef2</code></a>
Updating version.json and repo version numbers to: 26.1</li>
<li><a
href="https://github.com/protocolbuffers/protobuf/commit/49253b118b40719b938c2b74a53d70f5450d87b0"><code>49253b1</code></a>
Merge pull request <a
href="https://redirect.github.com/protocolbuffers/protobuf/issues/16308">#16308</a>
from protocolbuffers/cp-26x-3</li>
<li><a
href="https://github.com/protocolbuffers/protobuf/commit/9bf69ecc833757839421b89e92ddb4dc09b2af0d"><code>9bf69ec</code></a>
Fix validateFeatures to be called after resolved features are actually
set to...</li>
<li><a
href="https://github.com/protocolbuffers/protobuf/commit/b752bc2b93ea16b1ec19c9a7421f77a028d7ecdf"><code>b752bc2</code></a>
Merge pull request <a
href="https://redirect.github.com/protocolbuffers/protobuf/issues/16307">#16307</a>
from protocolbuffers/cp-26x-2</li>
<li><a
href="https://github.com/protocolbuffers/protobuf/commit/f7d23268df8a9e1ac4a9ac3a9178bba68e66e088"><code>f7d2326</code></a>
Merge pull request <a
href="https://redirect.github.com/protocolbuffers/protobuf/issues/16309">#16309</a>
from protocolbuffers/cp-26x-4</li>
<li><a
href="https://github.com/protocolbuffers/protobuf/commit/2e51ff6de3e8c594d965b2ad8952b911383cf0bf"><code>2e51ff6</code></a>
Cherry-pick required label handling in JRuby field descriptor from <a
href="https://gi">https://gi</a>...</li>
<li><a
href="https://github.com/protocolbuffers/protobuf/commit/a2f5303916d00725cbd63ee92445b330f70d71a6"><code>a2f5303</code></a>
Update cmake stalenes</li>
<li><a
href="https://github.com/protocolbuffers/protobuf/commit/6a177d2cf6d6eb0f4dc87426947252c9f5e7df2b"><code>6a177d2</code></a>
Merge branch '26.x' into cp-26x-4</li>
<li><a
href="https://github.com/protocolbuffers/protobuf/commit/2d3d8ba410550082ee20777653a2a1d515ff8036"><code>2d3d8ba</code></a>
Expand cpp_features_proto_srcs visibility</li>
<li><a
href="https://github.com/protocolbuffers/protobuf/commit/e1092ee6e0b7328d5d506d65322f0b15c5b08b21"><code>e1092ee</code></a>
Merge pull request <a
href="https://redirect.github.com/protocolbuffers/protobuf/issues/16294">#16294</a>
from protocolbuffers/cp-26x</li>
<li>Additional commits viewable in <a
href="https://github.com/protocolbuffers/protobuf/compare/v4.22.0-rc1...v5.26.1">compare
view</a></li>
</ul>
</details>
<br />

Dependabot will resolve any conflicts with this PR as long as you don't
alter it yourself. You can also trigger a rebase manually by commenting
`@dependabot rebase`.

[//]: # (dependabot-automerge-start)
[//]: # (dependabot-automerge-end)

---

<details>
<summary>Dependabot commands and options</summary>
<br />

You can trigger Dependabot actions by commenting on this PR:
- `@dependabot rebase` will rebase this PR
- `@dependabot recreate` will recreate this PR, overwriting any edits
that have been made to it
- `@dependabot merge` will merge this PR after your CI passes on it
- `@dependabot squash and merge` will squash and merge this PR after
your CI passes on it
- `@dependabot cancel merge` will cancel a previously requested merge
and block automerging
- `@dependabot reopen` will reopen this PR if it is closed
- `@dependabot close` will close this PR and stop Dependabot recreating
it. You can achieve the same result by closing it manually
- `@dependabot show <dependency name> ignore conditions` will show all
of the ignore conditions of the specified dependency
- `@dependabot ignore this major version` will close this PR and stop
Dependabot creating any more for this major version (unless you reopen
the PR or upgrade to it yourself)
- `@dependabot ignore this minor version` will close this PR and stop
Dependabot creating any more for this minor version (unless you reopen
the PR or upgrade to it yourself)
- `@dependabot ignore this dependency` will close this PR and stop
Dependabot creating any more for this dependency (unless you reopen the
PR or upgrade to it yourself)

</details>

pyproject.toml

@@ -37,7 +37,7 @@ dependencies = [
   "grpcio-tools >= 1.54.2, < 2",
   "networkx >= 2.8, < 4",
   "numpy >= 1.24.2, < 2",
-  "protobuf >= 4.21.6, < 5",
+  "protobuf >= 4.21.6, < 6",
   "pydantic >= 2.3, < 3",
   "timezonefinder >= 6.2.0, < 7",
   "tqdm >= 4.38.0, < 5",