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React version: 18.0.0-beta-149b420f6-20211119

## Steps To Reproduce

1. render a context with `react-test-renderer` (wrapped in act)
2. render the same context with `react-dom/server`

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Link to code example: https://codesandbox.io/s/react-18-react-test-renderer-react-dom-server-forked-lbs7j?file=/package.json:189-219
```js
const Context = React.createContext(null);

function Component({ renderer }) {
  return (
    <Context.Provider value={renderer}>
      <div />
    </Context.Provider>
  );
}

let testRendererRoot;
ReactTestRenderer.act(() => {
  testRendererRoot = ReactTestRenderer.create(
    <Component renderer="react-test-renderer" />
  );
});
ReactTestRenderer.act(() => {
  testRendererRoot.unmount();
});

ReactDOMServer.renderToString(<Component renderer="react-dom/server" />);
```

## The current behavior

`renderToString` results in the console error "Warning: Detected multiple renderers concurrently rendering the same context provider. This is currently unsupported."


## The expected behavior

No error like in React 17 (https://codesandbox.io/s/react-17-react-test-renderer-react-dom-server-yr8gx).
Considering all renders are wrapped in their corresponding `act` I don't expect that I'm concurrently rendering. 

I tried to understand when we reset the `rendererSigil` (responsible for checking if we "concurrently rendering") is reset and it seems like we never reset it but only initialize it when creating the context (`createContext`)
So it either seems like multiple renderers in the same module are not supported anymore or the reset is missing.


consumer.lanes = mergeLanes(consumer.lanes, renderLanes);
            const alternate = consumer.alternate;
            if (alternate !== null) {
              alternate.lanes = mergeLanes(alternate.lanes, renderLanes);
            }
            scheduleContextWorkOnParentPath(
              consumer.return,
              renderLanes,
              workInProgress,
            );
            if (!forcePropagateEntireTree) {
              
              
              
              
              nextFiber = null;
            }
            
            
            break findChangedDep;
          }
        }
        dep = dependency.next;
      }
    } else if (fiber.tag === DehydratedFragment) {