Download latest binary button links to the same URL for every OS type

Summary

Trying to download the runner leads to the same URL for each of the OS types, meaning macOS, Windows and Linux are pointed towards https://gitlab-runner-downloads.s3.amazonaws.com/latest/binaries/gitlab-runner-linux-amd64.

Steps to reproduce

1. Go to any project
2. Open CI/CD
3. Expand Runners section
4. Click on "Show runner registration information"
5. Hover over "Download latest binary" button
6. See that its the same for Windows, Linux and macOS

Example Project

Any project will do.

What is the current bug behavior?

The URL for the button is https://gitlab-runner-downloads.s3.amazonaws.com/latest/binaries/gitlab-runner-linux-amd64 for all 3 OS types.

What is the expected correct behavior?

Each OS should use its respective URL for the button:

• Windows: https://gitlab-runner-downloads.s3.amazonaws.com/latest/binaries/gitlab-runner-windows-amd64.exe
• macOS: https://gitlab-runner-downloads.s3.amazonaws.com/latest/binaries/gitlab-runner-darwin-amd64
• Linux: https://gitlab-runner-downloads.s3.amazonaws.com/latest/binaries/gitlab-runner-linux-amd64

Relevant logs and/or screenshots

Output of checks

This bug happens on GitLab.com

Results of GitLab environment info

Expand for output related to GitLab environment info

(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:env:info`)

(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production`)

Results of GitLab application Check

Expand for output related to the GitLab application check

(For installations with omnibus-gitlab package run and paste the output of:
sudo gitlab-rake gitlab:check SANITIZE=true)
(For installations from source run and paste the output of:
sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true)
(we will only investigate if the tests are passing)

Possible fixes