[EuiFlyout] Focus behaviour is different than expected with more than one Flyout open

**Describe the bug**

If only a single Flyout is open, the Flyout itself is focused on open and the next tab is the close button.
If another Flyout is open as well then the Flyout dialog seems to not be focused on open (instead the toggle button stays focused), meaning 2 tabs are needed to get to the close button.

**Impact and severity**
Impact is low because it's not blocking users, it's one more extra tab needed.

**Environment and versions**
- EUI version: v99
- React version: 18 (does not affect 17 nor 16)

**To Reproduce**
WIP

**Expected behavior**
Focus behaviour should be the same regardless of the amount of Flyouts open simultaneously.

**Additional context**
This one surfaced while testing EuiCollapsibleNavBeta functionality in [#8325](https://github.com/elastic/eui/pull/8325#discussion_r1973266414)