.Net: Bump xunit from 2.6.3 to 2.6.4 in /dotnet (microsoft#4425)

Bumps [xunit](https://github.com/xunit/xunit) from 2.6.3 to 2.6.4.
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/xunit/xunit/commit/0f87ff772a29aa3d4ef7cb5b34a8aeeaab2c2a28"><code>0f87ff7</code></a>
v2.6.4</li>
<li><a
href="https://github.com/xunit/xunit/commit/e466a7c13337a93c07da6b3480f6637c005ccdc9"><code>e466a7c</code></a>
Unit tests for <a
href="https://redirect.github.com/xunit/xunit/issues/2850">#2850</a>
(v2)</li>
<li><a
href="https://github.com/xunit/xunit/commit/0cc026be3bc3a9f97dda99194b72e13f597e791b"><code>0cc026b</code></a>
Add KeyValuePair tests with collections and IEquatable objects in the
key slot</li>
<li><a
href="https://github.com/xunit/xunit/commit/c729d7fd799c7db658b2a0f7bb6c27a9ef252934"><code>c729d7f</code></a>
Add collection dictionary tests for IEquatable&lt;&gt; objects in the
value slot</li>
<li><a
href="https://github.com/xunit/xunit/commit/0eb76d2b780819865a3291d24d4eced6ed744002"><code>0eb76d2</code></a>
Attempt to fix race condition reported in <a
href="https://github.com/visualstudio.xunit/issues/issues/396">visualstudio.xunit/issues#396</a></li>
<li><a
href="https://github.com/xunit/xunit/commit/348c56ddd3e877e821e9a9f59918a1fbbab3ad45"><code>348c56d</code></a>
Bump up to v2.6.4-pre</li>
<li>See full diff in <a
href="https://github.com/xunit/xunit/compare/2.6.3...2.6.4">compare
view</a></li>
</ul>
</details>
<br />


[![Dependabot compatibility
score](https://dependabot-badges.githubapp.com/badges/compatibility_score?dependency-name=xunit&package-manager=nuget&previous-version=2.6.3&new-version=2.6.4)](https://docs.github.com/en/github/managing-security-vulnerabilities/about-dependabot-security-updates#about-compatibility-scores)

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] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

dotnet/Directory.Packages.props

@@ -46,7 +46,7 @@
     <PackageVersion Include="Moq" Version="[4.18.4]" />
     <PackageVersion Include="System.Threading.Channels" Version="8.0.0" />
     <PackageVersion Include="System.Threading.Tasks.Dataflow" Version="8.0.0" />
-    <PackageVersion Include="xunit" Version="2.6.3" />
+    <PackageVersion Include="xunit" Version="2.6.4" />
     <PackageVersion Include="xunit.runner.visualstudio" Version="2.5.6" />
     <PackageVersion Include="xretry" Version="1.9.0" />
     <PackageVersion Include="coverlet.collector" Version="6.0.0" />