build: avoid CVE versions

Author: mfkl

src/LibVLCSharp/LibVLCSharp.csproj

@@ -92,6 +92,12 @@ LibVLC needs to be installed separately, see VideoLAN.LibVLC.* packages.</Descri
     <PackageReference Include="System.Memory" Version="4.5.4" />
   </ItemGroup>
 
+  <ItemGroup Condition=" '$(TargetFramework)' != 'net40' ">
+    <PackageReference Include="System.Net.Http" Version="4.3.4" />
+    <PackageReference Include="System.Private.Uri" Version="4.3.2" />
+    <PackageReference Include="System.Text.RegularExpressions" Version="4.3.1" />
+  </ItemGroup>
+
   <ItemGroup Condition="'$(TargetFramework)' == 'net471' Or '$(TargetFramework)' == 'netstandard2.0' ">
     <PackageReference Include="System.Memory" Version="4.6.0" />
   </ItemGroup>