Update assembly metadata format for Funding.GitHub

Since each sponsorable would need his own public/private key (most likely), we evolve the format to contain (in a single attribute) both the sponsorable login (after `Funding.GitHub` prefix) and the public key (as the metadata attribute value).

Author: kzu

src/Directory.Build.targets

@@ -116,8 +116,8 @@
   </ItemGroup>
 
   <ItemGroup Label="Sponsors">
-    <AssemblyMetadata Include="Funding.PublicKey" Value="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" />
-    <AssemblyMetadata Include="Funding.GitHub" Value="devlooped" />
+    <!-- Funding.GitHub.[sponsorable] = PublicKey -->
+    <AssemblyMetadata Include="Funding.GitHub.devlooped" Value="MIIBigKCAYEA5inhv8QymaDBOihNi1eY+6+hcIB5qSONFZxbxxXAyOtxAdjFCPM+94gIZqM9CDrX3pyg1lTJfml/a/FZSU9dB1ii5mSX/mNHBFXn1/l/gi1ErdbkIF5YbW6oxWFxf3G5mwVXwnPfxHTyQdmWQ3YJR+A3EB4kaFwLqA6Ha5lb2ObGpMTQJNakD4oTAGDhqHMGhu6PupGq5ie4qZcQ7N8ANw8xH7nicTkbqEhQABHWOTmLBWq5f5F6RYGF8P7cl0IWl/w4YcIZkGm2vX2fi26F9F60cU1v13GZEVDTXpJ9kzvYeM9sYk6fWaoyY2jhE51qbv0B0u6hScZiLREtm3n7ClJbIGXhkUppFS2JlNaX3rgQ6t+4LK8gUTyLt3zDs2H8OZyCwlCpfmGmdsUMkm1xX6t2r+95U3zywynxoWZfjBCJf41leM9OMKYwNWZ6LQMyo83HWw1PBIrX4ZLClFwqBcSYsXDyT8/ZLd1cdYmPfmtllIXxZhLClwT5qbCWv73VAgMBAAE=" />
   </ItemGroup>
 
   <Target Name="IsPackable" Returns="@(IsPackable)">