[Uptime] Test now is disabled for a monitor with both Public and Private Locations.

[awahab07]

Kibana version: 8.5.0 (Hasn't been tested on 8.4.0)

Elasticsearch version: 8.5.0

Describe the bug:
A synthetics monitor configured for both public and private locations, is only shown as a private monitor (fleet_managed: true) in uptime overview page. As a result, the Test now button (with play icon) on Uptime Monitors page is disabled for such a monitor.

Steps to reproduce:

1. Setup Kibana and cluster to have public as well as private locations. Set up agents as well as so that test results are available under Uptime -> Monitors Overview page.
2. Notice that the monitor does not have Test now button in front as if it is only a fleet managed monitor.
3. If Test now button is available, try running a test and observe the behavior afterwards. Or try to create a new monitor as it depends on which type of results comes at top.

Expected behavior:
For a monitor configured with both public and private locations, Test now button should be available.

Screenshots (if relevant):

Errors in browser console (if relevant):

Provide logs and/or server output (if relevant):

Any additional context:
Only the first fetched summary is passed to the TestNowColumn (as shown in the snippet below) which should be changed to consider all summaries to determine if monitor is only fleet_managed or both.

kibana/x-pack/plugins/synthetics/public/legacy_uptime/components/overview/monitor_list/monitor_list.tsx

Lines 211 to 215 in 81d7a6f

	<TestNowColumn
	monitorId={item.monitor_id}
	configId={item.configId}
	selectedMonitor={item.state.summaryPings[0]}
	/>

[elasticmachine]

Pinging @elastic/uptime (Team:uptime)