CI: move vpk and Velopack to 1.2.161, whose Gitea upload survives the forge's new release responses

The desktop nightly has failed on every push to main since 2 October, at 'publish the nightly
release'. vpk 1.2.0 creates the draft release and then reads release.Assets from the forge's
answer, which the upgraded server (28.0.0) no longer fills in for a new release, so it threw a
NullReferenceException at GiteaRepository.cs:136. The step deletes the previous nightly-desktop
release before it uploads, so desktop clients have had no nightly to update from since.

1.2.161 reads the assets null-safely. The library moves with the tool, since Velopack expects the
two to match. Every vpk option the workflow and the release scripts pass is present in 1.2.161;
the only renamed ones are two MSI options nothing here uses.

Directory.Packages.props

@@ -172,7 +172,7 @@
       constant rather than a setting: an operator who could answer the update check could pin a
       chosen user to a known-vulnerable build. See docs/adr/0013-desktop-distribution-and-updates.md.
     -->
-    <PackageVersion Include="Velopack" Version="1.2.0" />
+    <PackageVersion Include="Velopack" Version="1.2.161" />
 
     <!--
       Microsoft's own TPM 2.0 stack, TSS.MSR, and the only way LinuxDeviceKeyStore reaches the chip.