Bump clang-format from 18.1.8 to 21.1.8 (#3)

Bumps [clang-format](https://github.com/ssciwr/clang-format-wheel) from
18.1.8 to 21.1.8.
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/ssciwr/clang-format-wheel/commit/2d5d1c267873621d35d53e12d1d0ac206ab37654"><code>2d5d1c2</code></a>
v21.1.8</li>
<li><a
href="https://github.com/ssciwr/clang-format-wheel/commit/22ca0916280432fb6e63ebc9eb655212cc32d8af"><code>22ca091</code></a>
Merge pull request <a
href="https://redirect.github.com/ssciwr/clang-format-wheel/issues/150">#150</a>
from ssciwr/dependabot/github_actions/docker/setup-qe...</li>
<li><a
href="https://github.com/ssciwr/clang-format-wheel/commit/771aa87f1660f7d0d5c11dc2304d85d704aadc2b"><code>771aa87</code></a>
v21.1.7</li>
<li><a
href="https://github.com/ssciwr/clang-format-wheel/commit/825edabdd3254e9471e9ae74fd97fe1c0d3615da"><code>825edab</code></a>
Bump docker/setup-qemu-action from 3.6.0 to 3.7.0</li>
<li><a
href="https://github.com/ssciwr/clang-format-wheel/commit/5a145d8c30b46e3b8ee40bc43b63ecd480a1cae3"><code>5a145d8</code></a>
Merge pull request <a
href="https://redirect.github.com/ssciwr/clang-format-wheel/issues/149">#149</a>
from ssciwr/ci</li>
<li><a
href="https://github.com/ssciwr/clang-format-wheel/commit/3747556835f90484a7dad93c5288632011b32c12"><code>3747556</code></a>
Update deprecated macos-13 intel mac runner to use macos-15-intel, bump
actions</li>
<li><a
href="https://github.com/ssciwr/clang-format-wheel/commit/b43cdff14e76160d57e29eee774209b1b8834e8d"><code>b43cdff</code></a>
v21.1.6</li>
<li><a
href="https://github.com/ssciwr/clang-format-wheel/commit/303a117a34ac9402d792b42bcadcd78f933839c2"><code>303a117</code></a>
Merge pull request <a
href="https://redirect.github.com/ssciwr/clang-format-wheel/issues/148">#148</a>
from ssciwr/dependabot/github_actions/actions/downloa...</li>
<li><a
href="https://github.com/ssciwr/clang-format-wheel/commit/be0a06705c4918d2c1e3bd0be141efac7ba532a6"><code>be0a067</code></a>
Merge pull request <a
href="https://redirect.github.com/ssciwr/clang-format-wheel/issues/147">#147</a>
from ssciwr/dependabot/github_actions/actions/upload-...</li>
<li><a
href="https://github.com/ssciwr/clang-format-wheel/commit/3a3e2ec19292c87228a2817e96916c93df1129be"><code>3a3e2ec</code></a>
Merge pull request <a
href="https://redirect.github.com/ssciwr/clang-format-wheel/issues/145">#145</a>
from ssciwr/dependabot/github_actions/pypa/cibuildwhe...</li>
<li>Additional commits viewable in <a
href="https://github.com/ssciwr/clang-format-wheel/compare/v18.1.8...v21.1.8">compare
view</a></li>
</ul>
</details>
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Author: steve-downey

pyproject.toml

@@ -9,7 +9,7 @@ dependencies = []
 [dependency-groups]
 dev = [
     "cmake==4.2.1",
-    "clang-format==18.1.8",
+    "clang-format==21.1.8",
     "gcovr>=7.2",
     "pre-commit>=3.7.1",
 ]