Fixes tutorial installation link

[Voldivh]

🦟 Bug fix

Fixes https://github.com/gazebosim/gazebo_test_cases/issues/407 and https://github.com/gazebosim/gazebo_test_cases/issues/408

Summary

Fixes the url for the installation page.

Checklist

• [ ] Signed all commits for DCO
• [ ] Added tests
• [ ] Updated documentation (as needed)
• [ ] Updated migration guide (as needed)
• [ ] Consider updating Python bindings (if the library has them)
• [ ] codecheck passed (See contributing)
• [ ] All tests passed (See test coverage)
• [ ] While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[Voldivh]

Closing in favor of https://github.com/gazebosim/gz-tools/pull/124