Improve spacetime-install.ps1 (#3505)

# Description of Changes

<!-- Please describe your change, mention any related tickets, and so on
here. -->

This is a follow-up to
#2356 . Essentially we
want to remove this `return` statement so that you can both install the
vcruntime and also continue installing SpacetimeDB without having to run
the installer twice on Windows.

# API and ABI breaking changes

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corresponding GitHub label. -->

None

# Expected complexity level and risk

1 - this affects windows installation.

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# Testing

I tested this on a new Windows 11 install. You can test the script by
downloading it from this PR and then running the following:
```
iex (Get-Content .\spacetime-install.ps1 -Raw -Encoding UTF8)
```

- [x] I have tested this

This is from a brand-new Windows11 install with all updates installed:
<img width="971" height="328" alt="image"
src="https://github.com/user-attachments/assets/76e9b813-64f9-4a92-b961-c2136fa1372e"
/>

Then I opened a new terminal window:
<img width="815" height="162" alt="image"
src="https://github.com/user-attachments/assets/49e7cf95-fa37-4a5b-9fdd-7722e2055495"
/>

Signed-off-by: John Detter <4099508+jdetter@users.noreply.github.com>

Author: jdetter

crates/update/spacetime-install.ps1

@@ -28,7 +28,6 @@ function Install {
         $Installer = Join-Path ([System.IO.Path]::GetTempPath()) "vc_redist.x64.exe"
         Invoke-WebRequest $DownloadUrl -OutFile $Installer -UseBasicParsing
         Start-Process -Wait -FilePath $Installer -ArgumentList "/quiet", "/install"
-        return
     }
 
     $DownloadUrl = "https://github.com/clockworklabs/SpacetimeDB/releases/latest/download/spacetimedb-update-x86_64-pc-windows-msvc.exe"
@@ -54,4 +53,4 @@ function Install {
     Write-Output "We have added spacetimedb to your Path. You may have to logout and log back in to reload your environment."
 }
 
-Install
+Install