Updated configuration for the lychee link checker a.o.

[Evagan2018]

• Updated configuration for the lychee link checker
• Set max redirects to 2
• Added .lycheeignore file to filter out known false positive errors.

[Copilot]

Pull request overview

This PR updates the repository’s Lychee-based link-checking setup to reduce false positives and improve workflow stability/performance via caching and tighter redirect handling.

Changes:

• Add a .lycheeignore file to exclude known false-positive / environment-sensitive links.
• Update the link-check GitHub Actions workflow to include caching and set --max-redirects 2.
• Expand workflow triggers to run when Lychee configuration/workflow files change.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
.lycheeignore	Introduces ignore rules for known problematic links to reduce noisy failures.
.github/workflows/link-check.yml	Updates workflow triggers and Lychee invocation (caching, headers/UA, redirect limit).

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