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.

.config/dotnet-tools.json

@@ -10,7 +10,7 @@
       "rollForward": false
     },
     "vpk": {
-      "version": "1.2.0",
+      "version": "1.2.161",
       "commands": [
         "vpk"
       ],