fix: use feature branch for winget PRs (#1544)

* fix: use feature branch for winget PRs instead of master

GoReleaser was pushing manifest files directly to the master branch of
stripe/winget-pkgs, then PRing master->master. The winget-pkgs bot
rejects this. Use a versioned feature branch (e.g. stripe-cli-1.40.5)
so each release gets a clean PR.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Committed-By-Agent: claude

* fix: match existing winget package identifier casing

Use Stripe.StripeCli (PascalCase) to match the existing package in
winget-pkgs, not Stripe.StripeCLI.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Committed-By-Agent: claude

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Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>