MINOR: [C#] Bump xunit from 2.7.1 to 2.8.0 in /csharp (apache#41439)

Bumps [xunit](https://github.com/xunit/xunit) from 2.7.1 to 2.8.0.
<details>
<summary>Commits</summary>
<ul>
<li><a href="https://github.com/xunit/xunit/commit/be260b39de3f9f93868b479d83ba46393a44c4f2"><code>be260b3</code></a> v2.8.0</li>
<li><a href="https://github.com/xunit/xunit/commit/a8ceb66bd701ba6040474676a795ebdf0ab2a068"><code>a8ceb66</code></a> <a href="https://redirect.github.com/xunit/xunit/issues/783">#783</a>: Add -useansicolor flag to console runner (v2)</li>
<li><a href="https://github.com/xunit/xunit/commit/7b0ff93592ac5fdc28eb59aef85224ff44b3632a"><code>7b0ff93</code></a> Don't show /aggressive with unlimited threads</li>
<li><a href="https://github.com/xunit/xunit/commit/46cdf06273be4732f548669b1a23022016eeb0d8"><code>46cdf06</code></a> Support parallel algorithm in MSBuild runner</li>
<li><a href="https://github.com/xunit/xunit/commit/b4aa876e14399dbdbab92b3486ec32b8f1d55268"><code>b4aa876</code></a> Support multipler syntax in MSBuild runner</li>
<li><a href="https://github.com/xunit/xunit/commit/6790b481b2cdf5a0502e92e86336b42c9052851b"><code>6790b48</code></a> Add aggressive display to TestFrameworkEnvironment reported by XunitTestAssem...</li>
<li><a href="https://github.com/xunit/xunit/commit/3dd7e9146ed0881c17b2fd791dd30c7b649faa40"><code>3dd7e91</code></a> Update mocks to make CollectionBehaviorAttribute property values optional</li>
<li><a href="https://github.com/xunit/xunit/commit/4c82deae46743c3c54260747a626394f6f1514f8"><code>4c82dea</code></a> Asking for default threads should set 0, not null</li>
<li><a href="https://github.com/xunit/xunit/commit/d73cdefc96ac2bca3f3ed9aa2e5948af266c24a8"><code>d73cdef</code></a> Should not try to use a semaphore when we've been asked for unlimited threads</li>
<li><a href="https://github.com/xunit/xunit/commit/3722e542340412df626d76e0585bd2c6659fd5ea"><code>3722e54</code></a> Enable multiplier style max threads support</li>
<li>Additional commits viewable in <a href="https://github.com/xunit/xunit/compare/2.7.1...2.8.0">compare view</a></li>
</ul>
</details>
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Authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Signed-off-by: Curt Hagenlocher <[email protected]>

Author: dependabot[bot]

csharp/test/Apache.Arrow.Compression.Tests/Apache.Arrow.Compression.Tests.csproj

@@ -8,7 +8,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.9.0" />
-    <PackageReference Include="xunit" Version="2.7.1" />
+    <PackageReference Include="xunit" Version="2.8.0" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.8.0" />
   </ItemGroup>
 

csharp/test/Apache.Arrow.Flight.Sql.Tests/Apache.Arrow.Flight.Sql.Tests.csproj

@@ -7,7 +7,7 @@
 
     <ItemGroup>
       <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.9.0" />
-      <PackageReference Include="xunit" Version="2.7.1" />
+      <PackageReference Include="xunit" Version="2.8.0" />
       <PackageReference Include="xunit.runner.visualstudio" Version="2.8.0" />
       <PackageReference Include="coverlet.collector" Version="6.0.2" />
     </ItemGroup>

csharp/test/Apache.Arrow.Flight.Tests/Apache.Arrow.Flight.Tests.csproj

@@ -7,7 +7,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.9.0" />
-    <PackageReference Include="xunit" Version="2.7.1" />
+    <PackageReference Include="xunit" Version="2.8.0" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.8.0" />
     <PackageReference Include="coverlet.collector" Version="6.0.2" />
   </ItemGroup>

csharp/test/Apache.Arrow.Tests/Apache.Arrow.Tests.csproj

@@ -17,7 +17,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.9.0" />
-    <PackageReference Include="xunit" Version="2.7.1" />
+    <PackageReference Include="xunit" Version="2.8.0" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.8.0">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>