Content - Jekyll: Exclude méli-mélo meta.md files from site (#2747)

They were previously being generated into blank meta.html HTML pages (sometimes with invalid/broken-looking HTML).

This resolves it by omitting them. Doesn't prevent real pages from retrieving any content from them.

Examples of affected pages:
* https://wet-boew.github.io/GCWeb/méli-mélo/2021-05-steps/meta.html
* https://wet-boew.github.io/GCWeb/méli-mélo/th-vitality/meta.html
* https://wet-boew.github.io/gcweb-compiled-demos/méli-mélo-demos/gc-thématique/th-empathy/meta.html
* https://wet-boew.github.io/gcweb-compiled-demos/méli-mélo-demos/2025-12-mille-iles/2021-05-steps/meta.html

Author: EricDunsworth

_config.yml

@@ -113,3 +113,4 @@ exclude:
 - vendor/gems/
 - vendor/ruby/
 - ~sites/
+- méli-mélo*/**/meta.md