fix: correct workflow issues found during documentation validation

[q-soriarty]

Summary

Documentation validation of all new/modified workflows revealed the following issues:

Critical

1. aur.yml — pkgbuild input expects file path, not inline content
   The KSXGitHub/github-actions-deploy-aur@v3 action expects a file path (e.g. ./PKGBUILD), but we pass inline PKGBUILD content as a multi-line string. This will fail on next release.
   Fix: generate PKGBUILD to a file, pass the path.

2. copr.yml — heredoc indentation breaks INI config
   The cat > ~/.config/copr <<EOF block has leading whitespace on each line. The copr-cli INI parser will not parse [copr-cli] correctly.
   Fix: remove leading whitespace or use <<-EOF with tabs.

Minor

3. winget.yml — ubuntu-latest instead of ubuntu-slim
   Official winget-releaser examples use ubuntu-slim (lighter, faster).
   Fix: change runs-on.

4. bump-go.yml — missing setup-go step
   go mod edit and go mod tidy run without actions/setup-go. The runner default Go version may not match.
   Fix: add actions/setup-go@v6 before the update step.

[github-actions]

Closed by #197 (merged into develop).