Tests

Bump third_party/imgui/repo from `2860d7b` to `f5befd2` #1491

Job	Run time
Test Suites - Linux (no-ble-no-shell-tsan-clang)	5m 30s
Test Suites - Darwin (no-ble-no-shell-tsan-clang)	1h 43m 23s
Test Suites - Darwin (no-ble-no-shell-asan-clang)	1h 22m 28s
REPL Tests - Linux	6m 2s
REPL Tests - Darwin	0s
	3h 17m 23s

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