test(rss): fix commands_coverage assertion for the new <rss xmlns:atom> tag

Follow-up to the RSS-fidelity change: the `<rss version="2.0">` substring now
carries the xmlns:atom attribute, so match the open-tag prefix instead.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/nuwiki-lsp/tests/commands_coverage.rs

@@ -533,7 +533,7 @@ fn nuwiki_rss_writes_feed_file() {
     let path = export_ops::write_rss(&cfg, &entries).unwrap();
     assert!(path.ends_with("rss.xml"));
     let xml = std::fs::read_to_string(&path).unwrap();
-    assert!(xml.contains("<rss version=\"2.0\">"));
+    assert!(xml.contains("<rss version=\"2.0\""));
     // Newest entry listed first.
     let p12 = xml.find("2026-05-12").unwrap();
     let p10 = xml.find("2026-05-10").unwrap();