[Maps] Fix flaky test in maps geo file – remove exact assertion on approximate document count (elastic#241426)

Resolves elastic#234490
The link to Flaky Test Runner:
https://buildkite.com/elastic/kibana-flaky-test-suite-runner/builds/9709

### Summary
This PR fixes a flaky test in the maps geo file upload suite.
The test was asserting an exact document count (Found ~281 documents),
but due to MVT tile rendering, the number of documents may vary slightly
depending on the zoom level.

### Details
In some runs, the count fluctuated between ~280 and ~281, causing the
test to fail intermittently.

### Reasoning
The failing test screenshot showed a slightly different zoom level
compared to the local FTR environment.
To stabilize the test, I explicitly set the zoom level at the beginning
of the test to ensure consistent MVT data loading.

(cherry picked from commit 7943c3e)

Author: olapawlus

x-pack/platform/test/functional/apps/maps/group4/file_upload/geojson.js

@@ -54,6 +54,7 @@ export default function ({ getPageObjects, getService }) {
     });
 
     it('should add as document layer', async () => {
+      await maps.setView(0, 0, 1); //  set stable viewport to prevent flakiness caused by MVT tiles loading different data at varying zoom levels
       await geoFileUpload.addFileAsDocumentLayer();
       await maps.waitForLayersToLoad();