Bump extern/fmt from 686339f to d326c72 (#696)

Bumps [extern/fmt](https://github.com/fmtlib/fmt) from `686339f` to
`d326c72`.
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/fmtlib/fmt/commit/d326c7298ac6804dba9264624c9df920c084d6a0"><code>d326c72</code></a>
Fix conversion a surrogate pair (<a
href="https://redirect.github.com/fmtlib/fmt/issues/4095">#4095</a>)</li>
<li><a
href="https://github.com/fmtlib/fmt/commit/6e462b89aa22fd5f737ed162d0150e145ccb1914"><code>6e462b8</code></a>
Get rid of std::copy</li>
<li><a
href="https://github.com/fmtlib/fmt/commit/aff640c32f9ada045e4f8c289119fb104e5c4290"><code>aff640c</code></a>
Make fmt::appender implement std::output_iterator concept (<a
href="https://redirect.github.com/fmtlib/fmt/issues/4093">#4093</a>)</li>
<li><a
href="https://github.com/fmtlib/fmt/commit/e23fb6a8b48cf17bf24aef629916f94a42042945"><code>e23fb6a</code></a>
Apply clang-format</li>
<li><a
href="https://github.com/fmtlib/fmt/commit/16b3542f7ea47e8899da17709ce482e9ce273970"><code>16b3542</code></a>
Remove float_specs</li>
<li><a
href="https://github.com/fmtlib/fmt/commit/29d7e580598ecf7d3d5ecc6e8d5dfadba14cf132"><code>29d7e58</code></a>
Remove float_format</li>
<li><a
href="https://github.com/fmtlib/fmt/commit/919f7c5e7fcef52de47efcf85e811b4282d84da8"><code>919f7c5</code></a>
Reduce float_specs usage</li>
<li><a
href="https://github.com/fmtlib/fmt/commit/a80d668a52a92b67e01cdf59622454b31c4059c3"><code>a80d668</code></a>
Diagnose invalid precision</li>
<li><a
href="https://github.com/fmtlib/fmt/commit/707d7d923a117df956fe7adf762ec48ecc5d6b55"><code>707d7d9</code></a>
Apply coding conventions</li>
<li><a
href="https://github.com/fmtlib/fmt/commit/de6ed8df8b270e3d158d5550823ede30a6d90939"><code>de6ed8d</code></a>
Test alignment</li>
<li>Additional commits viewable in <a
href="https://github.com/fmtlib/fmt/compare/686339f7c12967975af0381eec7ca1a90af6bfcc...d326c7298ac6804dba9264624c9df920c084d6a0">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>

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>