Bump MessagePack and System.Memory in /src/net

Bumps [MessagePack](https://github.com/MessagePack-CSharp/MessagePack-CSharp) and System.Memory. These dependencies needed to be updated together.

Updates `MessagePack` from 2.5.192 to 3.0.300
- [Release notes](https://github.com/MessagePack-CSharp/MessagePack-CSharp/releases)
- [Commits](MessagePack-CSharp/MessagePack-CSharp@v2.5.192...v3.0.300)

Updates `System.Memory` from 4.5.5 to 4.5.5

---
updated-dependencies:
- dependency-name: MessagePack
  dependency-type: direct:production
  update-type: version-update:semver-major
- dependency-name: System.Memory
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

src/net/KNet.Serialization.MessagePack/KNet.Serialization.MessagePack.csproj

@@ -21,7 +21,7 @@
 		<PackageReference Include="System.Memory" Version="4.5.5" />
 	</ItemGroup>
 	<ItemGroup>
-	  <PackageReference Include="MessagePack" Version="2.5.192" />
+	  <PackageReference Include="MessagePack" Version="3.0.300" />
 	  <PackageReference Include="Microsoft.SourceLink.GitHub" Version="8.0.0">
 	    <PrivateAssets>all</PrivateAssets>
 	    <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>