Improve breadcrumb schema generation

[zeeZ]

What does this PR change? What problem does it solve?

When run with HUGO_UGLYURLS=true, the position count is wrong and a comma is missing between array elements, causing errors during minification.
This PR decouples position counting from (potentially skipped) bc_list array indices and length, making it slightly more robust.

Was the change discussed in an issue or in the Discussions before?

Also fixes #1441 and its reproducer, which shows the same behavior

PR Checklist

• This change adds/updates translations and I have used the template present here.
• I have enabled maintainer edits for this PR.
• I have verified that the code works as described/as intended.
• This change adds a Social Icon which has a permissive license to use it.
• This change does not include any CDN resources/links.
• This change does not include any unrelated scripts such as bash and python scripts.
• This change updates the overridden internal templates from HUGO's repository.

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud