ci: use separate token for homebrew tap

[0xRaghu]

Summary

• use the repo-scoped GitHub token for creating the mnemo GitHub Release
• pass HOMEBREW_TAP_PAT separately to GoReleaser's Homebrew tap repository config

Why

The v1.3.5 release run built binaries successfully but failed to create the GitHub Release because the Homebrew tap PAT did not have release permissions on Pilan-AI/mnemo.

Verification

• ruby -e 'require "yaml"; YAML.load_file(".github/workflows/release.yml"); YAML.load_file(".goreleaser.yml")'
• go run github.com/goreleaser/goreleaser/v2@v2.9.0 check
• go test ./...