Update libgit2 to v0.28.4

Author: ethomson

Diff for: LibGit2Sharp/LibGit2Sharp.csproj

@@ -29,7 +29,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="LibGit2Sharp.NativeBinaries" Version="[2.0.289]" PrivateAssets="none" />
+    <PackageReference Include="LibGit2Sharp.NativeBinaries" Version="[2.0.306]" PrivateAssets="none" />
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.0.0-beta-63127-02" PrivateAssets="all" />
     <PackageReference Include="Nerdbank.GitVersioning" Version="2.2.13" PrivateAssets="all" />
   </ItemGroup>