tadpole: Fix gitea oauth2 issuer URL

To have a trailing slash, which is expected of pre gitea 1.25
`tailscale` integrations

hosts/tadpole/modules/gitea/default.nix

@@ -67,6 +67,10 @@ in
           HTTP_PORT = 3001;
         };
 
+        oauth2 = {
+          JWT_CLAIM_ISSUER = "https://${gitDomain}/";
+        };
+
         database = {
           type = "sqlite3";
           passwordFile = config.age.secrets.gitea-dbpassword.path;