docs: fix broken and redirecting URLs in README.md - #407

Summary

Replaces 9 stale, redirecting, or non-HTTPS URLs in README.md with their current canonical targets. All links now resolve with HTTP 200 without any redirect hops.

Changes

• help.github.com/en/github/administering-a-repository/enabling-force-pushes-to-a-protected-branch → docs.github.com/en/github/administering-a-repository/enabling-force-pushes-to-a-protected-branch
• help.github.com/en/actions/building-actions/about-actions#versioning-your-action → docs.github.com/en/actions/building-actions/about-actions#versioning-your-action
• http://semver.org/ → https://semver.org/
• docs.github.com/en/github/getting-started-with-github/types-of-github-accounts → docs.github.com/en/get-started/learning-about-github/types-of-github-accounts
• docs.github.com/en/actions/managing-workflow-runs/skipping-workflow-runs → docs.github.com/en/actions/how-tos/manage-workflow-runs/skip-workflow-runs
• docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions#multiline-strings → docs.github.com/en/actions/reference/workflows-and-actions/workflow-commands#multiline-strings
• docs.github.com/en/github/administering-a-repository/disabling-or-limiting-github-actions-for-a-repository#enabling-workflows-for-private-repository-forks → docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/enabling-features-for-your-repository/managing-github-actions-settings-for-a-repository#enabling-workflows-for-private-repository-forks
• docs.github.com/en/free-pro-team@latest/actions/reference/events-that-trigger-workflows → docs.github.com/en/actions/reference/workflows-and-actions/events-that-trigger-workflows
• docs.github.com/en/github/authenticating-to-github/creating-a-personal-access-token → docs.github.com/en/authentication/keeping-your-account-and-data-secure/managing-your-personal-access-tokens

Motivation

GitHub has reorganized its documentation over time, leaving multiple links in the README pointing to paths that now return HTTP 301 redirects. Two links still used the legacy help.github.com domain. One link used plain http://. Stale links degrade the reader experience and may eventually break entirely if GitHub removes the redirect rules.

Impact

• Documentation-only change; no code, action behaviour, or configuration is affected.
• Fully backward compatible.

Testing

Each URL was verified with curl -L to confirm a final HTTP 200 response at the new target before being committed.