tools: improve v symlink -githubci diagnostic message, when used outside CIs or with sudo

[spytheman]

• ci: add check_symlink_works.yml
• ci, experiment: try using sudo ./v symlink -githubci, for linux and macos
• ci: remove sudo usage, improve the diagnostic message for sudo ./v symlink -githubci.
• ci: checkout appending to GITHUB_STEP_SUMMARY
• ci: use 🚀 for GITHUB_STEP_SUMMARY
• ci: use shell: bash for the windows job
• ci: use shell: bash for the windows task (shell: is not valid for the entire job)
• ci: use cd ~ with bash on windows too