[Search Sessions] Fix flaky partial results test in search examples (#155816)

## Summary

Unskip and fix flaky partial results test in search examples plugin.

Flaky test runner x100:
https://buildkite.com/elastic/kibana-flaky-test-suite-runner/builds/2172.

Fixes #116038.

### Checklist

- [ ] ~Any text added follows [EUI's writing
guidelines](https://elastic.github.io/eui/#/guidelines/writing), uses
sentence case text and includes [i18n
support](https://github.com/elastic/kibana/blob/main/packages/kbn-i18n/README.md)~
- [ ]
~[Documentation](https://www.elastic.co/guide/en/kibana/master/development-documentation.html)
was added for features that require explanation or tutorials~
- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios
- [ ] ~Any UI touched in this PR is usable by keyboard only (learn more
about [keyboard
accessibility](https://webaim.org/techniques/keyboard/))~
- [ ] ~Any UI touched in this PR does not create any new axe failures
(run axe in browser:
[FF](https://addons.mozilla.org/en-US/firefox/addon/axe-devtools/),
[Chrome](https://chrome.google.com/webstore/detail/axe-web-accessibility-tes/lhdoppojpmngadmnindnejefpokejbdd?hl=en-US))~
- [ ] ~If a plugin configuration key changed, check if it needs to be
allowlisted in the cloud and added to the [docker
list](https://github.com/elastic/kibana/blob/main/src/dev/build/tasks/os_packages/docker_generator/resources/base/bin/kibana-docker)~
- [ ] ~This renders correctly on smaller devices using a responsive
layout. (You can test this [in your
browser](https://www.browserstack.com/guide/responsive-testing-on-local-server))~
- [ ] ~This was checked for [cross-browser
compatibility](https://www.elastic.co/support/matrix#matrix_browsers)~

### For maintainers

- [ ] This was checked for breaking API changes and was [labeled
appropriately](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)

examples/search_examples/server/fibonacci_strategy.ts

@@ -8,6 +8,7 @@
 
 import { v4 as uuidv4 } from 'uuid';
 import { ISearchStrategy } from '@kbn/data-plugin/server';
+import { of } from 'rxjs';
 import { FibonacciRequest, FibonacciResponse } from '../common/types';
 
 export const fibonacciStrategyProvider = (): ISearchStrategy<
@@ -40,10 +41,7 @@ export const fibonacciStrategyProvider = (): ISearchStrategy<
       const took = Date.now() - started;
       const values = sequence.slice(0, loaded);
 
-      // Usually we'd do something like "of()" but for some reason it breaks in tests with the error
-      // "You provided an invalid object where a stream was expected." which is why we have to cast
-      // down below as well
-      return [{ id, loaded, total, isRunning, isPartial, rawResponse: { took, values } }];
+      return of({ id, loaded, total, isRunning, isPartial, rawResponse: { took, values } });
     },
     cancel: async (id: string) => {
       responseMap.delete(id);