[Fix] new clang -Wmissing-template-arg-list-after-template-kw warning (grpc#36805)

Clang now requires a template argument list after the use of the template keyword. Edit this
instance to remove the template keyword since there are no template arguments.

See llvm/llvm-project#80801.

Closes grpc#36805

COPYBARA_INTEGRATE_REVIEW=grpc#36805 from amykhuang:master 6f385be
PiperOrigin-RevId: 640554705

Author: amykhuang

src/core/lib/promise/detail/basic_seq.h

@@ -99,8 +99,7 @@ class BasicSeqIter {
           }
           cur_ = next;
           state_.~State();
-          Construct(&state_,
-                    Traits::template CallSeqFactory(f_, *cur_, std::move(arg)));
+          Construct(&state_, Traits::CallSeqFactory(f_, *cur_, std::move(arg)));
           return PollNonEmpty();
         });
   }