chore: add errata link

Add a link to errata on GitHub.

Author: marcoscaceres

index.html

@@ -42,6 +42,7 @@
       testSuiteURI: "https://wpt.live/geolocation-API/",
       implementationReportURI: "https://w3c.github.io/geolocation-api/reports/PR_imp_report.html",
       xref: "web-platform",
+      errata: "https://github.com/w3c/geolocation-api/labels/errata",
     };
     </script>
   </head>