Agent failing because of missing Microsoft.WindowsDesktop.App folder

For months, our Crank agent have been plagued with an issue where all jobs suddenly start failing with the message:
```
dotnet-install could not install a component:
```
After restarting the crank agent, the error mysteriously disappears until the next time.

I finally took some time to dig into it, and I found the root exception:

```
0:000> !pe 12ae1416148
Exception object: 0000012ae1416148
Exception type: System.IO.DirectoryNotFoundException
Message: Could not find a part of the path 'C:\Windows\TEMP\benchmarks-agent\benchmarks-server-4776\bnwqqose.b5j\shared\Microsoft.WindowsDesktop.App'.
InnerException:
StackTrace (generated):
SP IP Function
0000000E6D8FD450 00007FF7F5FCC6EC System_Private_CoreLib!System.IO.Enumeration.FileSystemEnumerator`1[[System.__Canon, System.Private.CoreLib]].CreateDirectoryHandle(System.String, Boolean)+0xbc
0000000E6D8FD4B0 00007FF7F5FCC534 System_Private_CoreLib!System.IO.Enumeration.FileSystemEnumerator`1[[System.__Canon, System.Private.CoreLib]].Init()+0x24
0000000E6D8FD510 00007FF7F608BF1D System_Private_CoreLib!System.IO.Enumeration.FileSystemEnumerableFactory.UserDirectories(System.String, System.String, System.IO.EnumerationOptions)+0x12d
0000000E6D8FD560 00007FF7F605770E System_Private_CoreLib!System.IO.Directory.InternalEnumeratePaths(System.String, System.String, System.IO.SearchTarget, System.IO.EnumerationOptions)+0x8e
0000000E6D8FD5A0 00007FF7F608BD47 System_Private_CoreLib!System.IO.Directory.GetDirectories(System.String)+0x47
0000000E6D8FD5E0 00007FF7F5AB62DD crank_agent!Microsoft.Crank.Agent.Startup.SeekCompatibleDesktopRuntime(System.String, System.String, System.String)+0x5d
0000000E6D8FD650 00007FF7F5A68BE1 crank_agent!Microsoft.Crank.Agent.Startup+d__78.MoveNext()+0x2061
```

My understanding is that Crank tries to install the .net runtime (https://github.com/dotnet/crank/blob/0042d4d1ecf64fee757c6739bda0c9fec8f19714/src/Microsoft.Crank.Agent/Startup.cs#L2747) and it sometimes fails (I assume because of a transient network error). When that happens, the version is added to an ignore list, then `SeekCompatibleDesktopRuntime` is used as fallback:

```
// Record that we don't need to try to download this version next time
_ignoredDesktopRuntimes.Add(desktopVersion);

// if the specified SDK can't be installed

// Seeking already installed Desktop runtimes
// c.f. https://github.com/dotnet/sdk/issues/4237

desktopVersion = SeekCompatibleDesktopRuntime(dotnetHome, targetFramework, desktopVersion);
```

And `SeekCompatibleDesktopRuntime` fails because of the aforementioned error (`Could not find a part of the path 'C:\Windows\TEMP\benchmarks-agent\benchmarks-server-4776\bnwqqose.b5j\shared\Microsoft.WindowsDesktop.App'.`).

Past this point, all jobs will fail because the target version has been added to `_ignoredDesktopRuntimes` so the agent will always use the bogus fallback.

I'm not sure what's the best way to fix it, but I would have a few recommendations:
- The job error should mention the exception, for easier debugging: https://github.com/dotnet/crank/blob/0042d4d1ecf64fee757c6739bda0c9fec8f19714/src/Microsoft.Crank.Agent/Startup.cs#L2919
- The version of the framework shouldn't be added to `_ignoredDesktopRuntimes` if the cause of the failure is a network error (assuming that can be detected)
- `SeekCompatibleDesktopRuntime` should check if the `Microsoft.WindowsDesktop.App` directory exists

But I'm still failing to understand why this directory doesn't exist to begin with. Maybe it has something to do with https://github.com/dotnet/sdk/issues/4237?