refactor: use explicit url for goatcounter

[kungfux]

Type of change

• Bug fix (non-breaking change which fixes an issue)

Description

Explicit GoatCounter URL was changed to a protocol-relative URL while doing refactoring #1543 which causes issues.

Run bundle exec htmlproofer _site \
Running 3 checks (Scripts, Links, Images) in ["_site"] on *.html files...

Checking [18](https://github.com/kungfux/kungfux.github.io/actions/runs/8101471704/job/22141725592#step:6:19)0 internal links
Checking internal link hashes in [19](https://github.com/kungfux/kungfux.github.io/actions/runs/8101471704/job/22141725592#step:6:20) files
Ran on 88 files!


For the Scripts check, the following failures were found:

* At _site/404.html:1:

  script link //gc.zgo.at/count.js is a protocol-relative URL, use explicit https:// instead

* At _site/about/index.html:51:

  script link //gc.zgo.at/count.js is a protocol-relative URL, use explicit https:// instead
...

Additional context

This is not released yet and introduced by #1543

[cotes2020]

Yeah, I was referring to the GoatCounter official docs at #1543, thanks for the fix.

[cotes2020]

Please consider using a refactor type for the commit message, so that we don't leave this extra record in changelog.

[github-actions]

🎉 This PR is included in version 7.0.0 🎉

The release is available on:

• v7.0.0
• GitHub release

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