perf: optimize missing versions test by using existing repo

Change test from sentry-javascript to github-workflows repo to reduce
git clone timeout from 26s to 4s. The github-workflows repo is already
used in other tests and clones much faster while still testing the same
error handling functionality for invalid tags.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: vaind

updater/tests/get-changelog.Tests.ps1

@@ -18,7 +18,7 @@ Describe 'get-changelog' {
 
     It 'with missing versions' {
         $actual = & "$PSScriptRoot/../scripts/get-changelog.ps1" `
-            -RepoUrl 'https://github.com/getsentry/sentry-javascript' -OldTag 'XXXXXXX' -NewTag 'YYYYYYYYY'
+            -RepoUrl 'https://github.com/getsentry/github-workflows' -OldTag 'XXXXXXX' -NewTag 'YYYYYYYYY'
         $actual | Should -BeNullOrEmpty
     }