Write-Host behaviour when using runspaces

At first I thought that there was a bug preventing the use of runspaces, but it seems that when invoking a runspace `Write-Host` just stops producing any output.

I have made below http trigger that creates and invokes 10 runspaces. After the first is invoked `Write-Host` stops "working"

```powershell
using namespace System.Net

# Input bindings are passed in via param block.
param($Request, $TriggerMetadata)

# setup runspace
Write-Host "Setting up runspace"
$sessionstate = [system.management.automation.runspaces.initialsessionstate]::CreateDefault()

$runspacepool = [runspacefactory]::CreateRunspacePool(1, [int]$env:NUMBER_OF_PROCESSORS+1, $sessionstate, $Host)
$runspacepool.Open()

$runspaces = [System.Collections.ArrayList]::new()
for ($i = 0; $i -lt 10; $i++) {
Write-Host "Creating runspace..."
$runspace = [powershell]::Create()
$runspace.RunspacePool = $runspacepool
$null = $runspace.AddScript({
Start-Sleep -Milliseconds 750
})
Write-Host "Invoking runspace"
$runspaces.Add([PSCustomObject]@{ Pipe = $runspace; Status = $runspace.BeginInvoke() })
# after this Write-Host does not produce any output
Write-Host "Runespace invoked"
}

Write-Host "Waiting for runspaces to complete"
while($runspaces.Status.IsCompleted -contains $false){Start-Sleep -Milliseconds 25}
Write-Host "Runspaces completed"

$RunspacesCompleted = ($runspaces.Status | Where-Object {$_.IsCompleted}).Count

# Associate values to output bindings by calling 'Push-OutputBinding'.
Push-OutputBinding -Name Response -Value ([HttpResponseContext]@{
StatusCode = [HttpStatusCode]::OK
Body = "Test completed $RunspacesCompleted runspaces"
})
```

The function does return `Test completed 10 runspaces` so everything seems to complete running.

This is by no means a critical error, but I would expect others using runspaces to become fairly confused as I did.
It also makes it much more complicated to follow along what is happening in the code.

Start by running the provided Azure Functions PowerShell HTTP-trigger example and observe the Write-Host output before and after BeginInvoke on the runspace pool. No repository files or tests are named, so investigate the function host's PowerShell logging and runspace handling. Done means the output behavior is explained and either corrected or documented with a regression check.

Written by the indexing model from the issue text.