Fix link checking, ignore top-level /api alias

Author: chalin

.htmltest.yml

@@ -25,7 +25,7 @@ IgnoreDirs:
 IgnoreInternalURLs: # list of paths
 IgnoreURLs: # list of regexs of paths or URLs to be ignored
   - /index.xml$ # Ignore rel="alternative" links to RSS feeds
-  - ^/api$
+  - ^/api/?$
   - ^((/..)?/docs/languages/\w+|\.\.)/(api|examples|registry)/$
   - ^(/..)?/docs/collector/registry/$
   - ^(/..)?/docs/languages/net/(metrics-api|traces-api)/