build(deps): Bump MSTest from 3.6.3 to 3.6.4 in the all group

Bumps the all group with 1 update: [MSTest](https://github.com/microsoft/testfx).


Updates `MSTest` from 3.6.3 to 3.6.4
- [Release notes](https://github.com/microsoft/testfx/releases)
- [Changelog](https://github.com/microsoft/testfx/blob/main/docs/Changelog.md)
- [Commits](microsoft/testfx@v3.6.3...v3.6.4)

---
updated-dependencies:
- dependency-name: MSTest
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: all
...

Signed-off-by: dependabot[bot] <[email protected]>

src/tests/IntegrationTests/Ultravox.IntegrationTests.csproj

@@ -5,7 +5,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="MSTest" Version="3.6.3" />
+    <PackageReference Include="MSTest" Version="3.6.4" />
     <PackageReference Include="GitHubActionsTestLogger" Version="2.4.1">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>