Fix copyright field rendering in RSS feed

[KonishchevDmitry]

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

The copyright is rendered in footer as {{ site.Copyright | markdownify }} which assumes it to be Markdown text, but RSS feed template doesn't ready for Markdown now.

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

No.

PR Checklist

• [ ] This change adds/updates translations and I have used the template present here.
• [x] I have enabled maintainer edits for this PR.
• [x] 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.
• [x] This change does not include any CDN resources/links.
• [x] This change does not include any unrelated scripts such as bash and python scripts.
• [x] This change updates the overridden internal templates from HUGO's repository.

[sonarcloud[bot]]

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