ci(release): Fetch the last 20 commits, not just 1 (#22152)

This should fix the merge error we encountered in the last release: https://github.com/getsentry/sentry/runs/1413845407?check_suite_focus=true#step:10:41

.github/workflows/release.yml

@@ -46,6 +46,7 @@ jobs:
       - uses: actions/checkout@v2
         with:
           token: ${{ secrets.GH_SENTRY_BOT_PAT }}
+          fetch-depth: 20
       - id: set-git-user
         name: Set git user to getsentry-bot
         run: |