[Fix] new clang -Wmissing-template-arg-list-after-template-kw warning (#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 https://github.com/llvm/llvm-project/pull/80801.

Closes #36805

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/36805 from amykhuang:master 6f385be2a0
PiperOrigin-RevId: 640554705

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();
         });
   }