Indexing a tree by path yields different result with trailing slash

When a slash is included when indexing into a tree to a subtree, the resulting TreeEntry has a path with a duplicated last path part.

using System.Text;
using LibGit2Sharp;

var path = Path.Combine(Path.GetTempPath(), Guid.NewGuid().ToString());

using var repo = new Repository(Repository.Init(path, isBare: true));

var bytes = Encoding.UTF8.GetBytes("Hello, World!");

var blob = repo.ObjectDatabase.CreateBlob(new MemoryStream(bytes));

var td = new TreeDefinition();
td.Add("some/deeply/nested/file", blob, Mode.NonExecutableFile);

var tree = repo.ObjectDatabase.CreateTree(td);

var withSlash = tree["some/deeply/"].Path;
var withoutSlash = tree["some/deeply"].Path;

Console.WriteLine(withSlash);       // some/deeply/deeply
Console.WriteLine(withoutSlash);    // some/deeply

I was seeing this across Linux and Windows, on versions 0.31 and 0.32 and .NET 10 and Framework 4.8

Reproduce the discrepancy using the provided TreeDefinition and tree indexer example, comparing the paths returned for "some/deeply/" and "some/deeply". Trace the TreeEntry path construction for indexed subtrees and add a regression test covering both inputs. Done means trailing-slash indexing returns the same non-duplicated path as the equivalent path without the slash.