fix(react): set fetching to the lack or presence of source

[JoviDeCroock]

Resolves #2648

Summary

When we changes variables onEnd seems to fire later than us establishing the new connection, this means we set fetching to a truthy value and then switch it off as we assume that we aren't fetching anymore.

Now when a subscription ends we check whether there is a new source already and base our fetching state off that, sandbox

CC @elias-pap

Set of changes

• rely on source to flip fetching state

[changeset-bot]

🦋 Changeset detected

Latest commit: 25c5cdf

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
urql	Patch

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[elias-pap]

This change might have introduced a different bug. I use wonka's fromPromise to mock executeSubscription on testing when creating a mock urql client, like this:

executeSubscription: ({ query, variables }) =>
      executeMockOperation({ schemaWithMocks, query, variables }),

const executeMockOperation = ({ schemaWithMocks, query, variables }) => {
  const result = graphql({
    schema: schemaWithMocks,
    source: query.loc.source.body,
    variableValues: variables,
  });
  return fromPromise(result);
};

Before the fix (3.0.2) fetching is eventually set to false when the data comes (expected). After the fix (3.0.3) fetching is set to true and never turns false again. I had to implement a custom source with makeSubject to work around this.