[select] Fix Select not respecting shouldDismissPopover={false} on Enter

[dokson]

Summary

Fixes #8079.

When a MenuItem is selected via keyboard (Enter), event.target is the <input> element rather than the menu item. The existing target.closest('.bp6-menu-item') therefore returned null, the dismiss check fell back to its default of true, and the popover always closed — ignoring shouldDismissPopover={false}.

This change adds a fallback in Select.handleItemSelect that looks up the active menu item (.bp6-menu-item.bp6-active) when the event target is not inside a menu item, so shouldDismissPopover is respected in both click and keyboard flows.

Reproduction from the issue: https://codesandbox.io/p/devbox/exciting-payne-swcdjy

Test plan

• Existing select.test.tsx suite passes (165 tests)
• New regression test: simulate keydown+keyup Enter on the input, assert popover stays open when shouldDismissPopover={false}

[palantirtech]

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Description

[select] Fix Select not respecting shouldDismissPopover={false} on Enter

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