MINOR: [C#] Bump ZstdSharp.Port and System.Runtime.CompilerServices.Unsafe in /csharp (apache#41440)

Bumps [ZstdSharp.Port](https://github.com/oleg-st/ZstdSharp) and [System.Runtime.CompilerServices.Unsafe](https://github.com/dotnet/runtime). These dependencies needed to be updated together.
Updates `ZstdSharp.Port` from 0.7.6 to 0.8.0
<details>
<summary>Release notes</summary>
<p><em>Sourced from <a href="https://github.com/oleg-st/ZstdSharp/releases">ZstdSharp.Port's releases</a>.</em></p>
<blockquote>
<h2>0.8.0</h2>
<p>Ported zstd v1.5.6
Workaround for .NET Native</p>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a href="https://github.com/oleg-st/ZstdSharp/commit/e0047696aec13703b3e99e4e9c74c85072ad7086"><code>e004769</code></a> 0.8.0</li>
<li><a href="https://github.com/oleg-st/ZstdSharp/commit/2704150c133edaeb5bb6a5654eda0be2c990fa3d"><code>2704150</code></a> Workaround for .NET Native</li>
<li><a href="https://github.com/oleg-st/ZstdSharp/commit/106a59ac8dbaa91016852681fb6cf20548cd5c11"><code>106a59a</code></a> SSE2/ARM code updated</li>
<li><a href="https://github.com/oleg-st/ZstdSharp/commit/c1171b8de7ea42f080180b3ef74777f93be6ee20"><code>c1171b8</code></a> Update packages</li>
<li><a href="https://github.com/oleg-st/ZstdSharp/commit/b44a2d6398b6cfaede0b5e709ef04c519d0e56a1"><code>b44a2d6</code></a> Fold some code blocks</li>
<li><a href="https://github.com/oleg-st/ZstdSharp/commit/b8b60c2aa5738535e21d058cab28f8ac024b2537"><code>b8b60c2</code></a> Ported zstd v1.5.6</li>
<li><a href="https://github.com/oleg-st/ZstdSharp/commit/2b8482888a01609069926fa4ba47118219707f92"><code>2b84828</code></a> Update benchmarks</li>
<li>See full diff in <a href="https://github.com/oleg-st/ZstdSharp/compare/0.7.6...0.8.0">compare view</a></li>
</ul>
</details>
<br />

Updates `System.Runtime.CompilerServices.Unsafe` from 4.7.1 to 6.0.0
<details>
<summary>Release notes</summary>
<p><em>Sourced from <a href="https://github.com/dotnet/runtime/releases">System.Runtime.CompilerServices.Unsafe's releases</a>.</em></p>
<blockquote>
<h2>.NET 6.0</h2>
<p><a href="https://github.com/dotnet/core/releases/tag/v6.0.0">Release</a></p>
<h2>.NET 6.0 RC 2</h2>
<p><a href="https://github.com/dotnet/core/tree/v6.0.0-rc.2">Release</a></p>
<h2>.NET 6.0 RC 1</h2>
<p><a href="https://github.com/dotnet/core/tree/v6.0.0-rc.1">Release</a></p>
<h2>.NET 6.0 Preview 7</h2>
<p><a href="https://github.com/dotnet/core/releases/tag/v6.0.0-preview.7">Release</a></p>
<h2>.NET 6.0 Preview 6</h2>
<p><a href="https://github.com/dotnet/core/releases/tag/v6.0.0-preview.6">Release</a></p>
<h2>.NET 6.0 Preview 5</h2>
<p><a href="https://github.com/dotnet/core/releases/tag/v6.0.0-preview.5">Release</a></p>
<h2>.NET 6.0 Preview 4</h2>
<p><a href="https://github.com/dotnet/core/releases/tag/v6.0.0-preview.4">Release</a></p>
<h2>.NET 6.0 Preview 3</h2>
<p><a href="https://github.com/dotnet/core/releases/tag/v6.0.0-preview.3">Release</a></p>
<h2>.NET 6.0 Preview 2</h2>
<p><a href="https://github.com/dotnet/core/releases/tag/v6.0.0-preview.2">Release</a></p>
<h2>.NET 6.0 Preview 1</h2>
<p><a href="https://github.com/dotnet/core/releases/tag/v6.0.0-preview.1">Release</a></p>
<h2>.NET 5.0.17</h2>
<p><a href="https://github.com/dotnet/core/tree/v5.0.17">Release</a></p>
<p>.NET 5 is now <a href="https://docs.microsoft.com/en-us/lifecycle/products/microsoft-net-and-net-core">out of support</a>. We recommend using .NET 6.</p>
<h2>.NET 5.0.16</h2>
<p><a href="https://github.com/dotnet/core/tree/v5.0.16">Release</a></p>
<h2>.NET 5.0.15</h2>
<p><a href="https://github.com/dotnet/core/tree/v5.0.15">Release</a></p>
<h2>.NET 5.0.14</h2>
<p><a href="https://github.com/dotnet/core/releases/tag/v5.0.14">Release</a></p>
<h2>.NET 5.0.13</h2>
<p><a href="https://github.com/dotnet/core/releases/tag/v5.0.13">Release</a></p>
<h2>.NET 5.0.11</h2>
<p><a href="https://github.com/dotnet/core/tree/v5.0.11">Release</a></p>

</blockquote>
<p>... (truncated)</p>
</details>
<details>
<summary>Commits</summary>
<ul>
<li>See full diff in <a href="https://github.com/dotnet/runtime/commits/v6.0.0">compare view</a></li>
</ul>
</details>
<br />

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csharp/src/Apache.Arrow.Compression/Apache.Arrow.Compression.csproj

@@ -13,7 +13,7 @@
 
   <ItemGroup>
     <PackageReference Include="K4os.Compression.LZ4.Streams" Version="1.3.8" />
-    <PackageReference Include="ZstdSharp.Port" Version="0.7.6" />
+    <PackageReference Include="ZstdSharp.Port" Version="0.8.0" />
   </ItemGroup>
 
   <ItemGroup>