Fix .md URLs redirecting instead of serving markdown (#60120)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: heiskr

src/shielding/middleware/handle-invalid-paths.ts

@@ -89,6 +89,7 @@ export default function handleInvalidPaths(
     return res.redirect(newUrl)
   } else if (req.path.endsWith('.md')) {
     req.url = req.url.replace(/\.md($|\?)/, '$1')
+    req.originalUrl = req.originalUrl.replace(/\.md($|\?)/, '$1')
     req.headers.accept = 'text/markdown'
     return next()
   }

src/shielding/tests/shielding.ts

@@ -77,6 +77,7 @@ describe('index.md and .md suffixes', () => {
     {
       const res = await get('/en/get-started.md')
       // Should not redirect — serves markdown directly (or 404 if page doesn't exist)
+      expect(res.statusCode).not.toBe(301)
       expect(res.statusCode).not.toBe(302)
     }
   })